I agree with the idea of raising rhinos on the beef/dairy cattle model, but there are a couple of potential glitches.

No matter how widely dispersed the population is, we can't really "expand" the gene pool--that is going to be limited by the size of the population some years back, when the population was around 100 individuals (with many of them being related). The best that can be hoped for is to preserve the remaining genetic variability by expanding the population through breeding every individual as widely as possible.

This genetic goal conflicts with the economic model used. Rhino horns can only be harvested once; after that, it has no economic value other than as breeding stock. In cattle, this is solved by using females and a limited number of males for breeding--"surplus" males, of course, are castrated (removing them from the gene pool) and used for beef. This isn't a problem with cattle due to the size of the cattle gene pool, but that model does cause problems when you begin with a small gene pool.

In animals like pure-bred dogs, this is a well-known problem. Starting from an already-limited gene pool (due to closed breed books), followed by breeding (most) females to a limited number of males, eventually results in a highly-inbred population. In turn, this can result in the surfacing of a number of previously-rare or unknown genetic problems, such as high rates of orthopedic problems or propensities toward various cancers.

We can see a wild example of the same thing in the problems found in cheetahs. Low sperm counts/motility and other breeding problems, susceptibility to various diseases, and deformities like bent limbs and cramped teeth. These problems are believed to be a result of a past genetic bottleneck, probably back in the last ice age. Cheetahs show that in the right environment this isn't a totally limiting factor for the survival of the species, but it sure doesn't help.