I think that not only would this in the long run not solve the Fulani Herdsmen issue, but it would infact worsen it, in the long run at least.

1. We have the fact that this is a one way solution, not only favouring instigators but very critically, doing nothing to punish the murderers among the Fulani herdsmen. This would become a great source for instigation of violence and hatred by host communities as they would feel the settlements are unjust, cruel and a reward for crime, which would no doubt fan the flames for further strife

2. Due to this idea heavily favouring the Fulani, the host communities are heavily inclined to be uncooperative and even if the governours are bribed into accepting this deal, the actual host communities are not going to be happy with it. The settlements would also more than likely take some valuable fertile lands from farmers given how much land would be needed for so many Fulani people and livestock to use, as their method of raising livestock is very lands inefficient and cows quickly graze a region to nothing if left on the same land for a long period, that is why they have to be constantly migrating around with their cattle, as such for their nomadic life style large swathes of farmer usable lands must be sacrificed. Both of these would breed future resentment, as they locals see the Fulani as land grabbing conquerors and the Fulani see the locals as greedy and wanting them to starve

3. The Population, Climate and Culture problems.

3a. First with population the poorer Fulani population that would be housed in these settlements are stuck at the 2nd phase of the Short notes on the five essential stages of Demographic cycle, as shown in this article http://www.preservearticles.com/articles/short-notes-on-the-five-essential-stages-of-demographic-cycle/5444, while every other population in Nigeria is stuck either in 2.5, 3, 4 or 5 as such they have a very high population, this would mean that their population grows much faster than that of their host, but while this sounds bad the main problem is that in a few generations, maybe even less than 50 years the Fulani and cow population rises so much that the settlements are no longer enough and they start demanding more or larger settlements, but by this time the host population would have grown enough that, while growing slower than the Fulani population, it would still be large enough that there would be no more land to give. The 50 year period is even an over exaggeration as given the hospitals and other health care serves to be constructed there, this would allow their population to rise even faster. Also the Fulani presence would mean that the host population cannot grow as much as it is stifled by competition with the Fulani and the total Fulani population is allowed to thrive while the population potential of other groups suffer

3b. The Climate problem is that, combined with population are the original source of the Fulani herdsmen issue, as the combination of a hotter climate caused by climate change and overgrazing resulting is less grazing land and increased Fulani and cow population caused by better healthcare, which ironically caused the over grazing that destroys their grazing lands, would mean that combined with population increase, the RUGA lands would quickly become unable to support the Funali that would then require more lands

3c. The Culture problem, as the RUGA population grows the host community would start noticing more and more children begging in the street, especially at noon, these are the Almajiri. They would start seeing seemingly homeless elderly people in the streets and disabled people sometimes with children, who seem to have no family, as the settlers become more comfortable they would start seeing imams coming to their houses to demand donations to their Almajiri schools, they woulds start seeing fights over sharia law being implemented in and around the settlements. Nigerians are not one and the culture of North and South are very different, with the eventual population growth in the settlements many of them would be forced to move to the Neighboring cities to look for jobs and there not only would all the boiling over hatred be expressed, but cultures would clash and almajiri children disturbing people for alms would be slapped, and pastors refusing to sponsor almajiri or going to preach would be killed, as seen with Mrs. Eunice Elisha, with the growth of the Fulani population and the self segregation between them and their host, there would be periodic massacres, first against their host and then retaliations against the settlements, thousands would die and this would make the settlers lose faith in the government and start demanding their own separate local and communal governours, which the locals would basically see as the "Invaders" taking over a piece of their lands. We all know this is where it would go with most of the settlements and must do something reasonable to stop it before it starts

4. I recently listened to a Youtube documentary on the Abbasid revolution, link here
https://www.youtube.com/watch?v=_MdITJvZymo&t=1724s , which touches on how the Arab conquerors of Persia constructed garrison towns for themselves next to the Persian cities, from there when ever the Persians revolt or attempt to free themselves, the Arabs (Almost entire a warrior Caste by now) go out, fight and subjugate the Persian cities and keep their control. While this is not the current purpose of the RUGA settlements, this is what any savvy Fulani politician like Buhari would turn them into, we have video evidence of Buhari instigating his supporters to violence if he did not win during the 2015 election and what better way to scare a population into supporting you than by basically having an armed and ready Garrison with a population close to theirs in every significant population centre of the opposition.

5. Since Buhari continues to lie that no herdsman carries guns, it no doubt means that these settlements would in no doubt come with their own military security force to "Protect Them", but whether that sentiment is true or not it would still mean a sizable detachment of Fulani soldiers neither loyal nor sympathetic to the host population, but loyal to the FG, Army and most importantly the Fulani Herdsmen, so that any conflict between the settlers and the host community, the settlers would have the backing of an army and this makes the problem in 4. even worse. While there are already many Fulani soldiers in the South and East, these people are forced to some what integrate and do not have to decide between their loyalty to the tribe or their duty to protect, and do not have a large population of their people constantly making them to be nepotistic

Interesting