Don't know how it works in NV, but in CA, FSP trucks are private tow companies that provide the service under contract. I'd suspect dealing with getting a bunch of independant private companies to drop the $$ on the radios needed, and then all the bother of getting them set up on the system is too much effort, never mind the issues of having private businesses on a public radio system.
In CA, near as I can tell, most all the FSP dispatching seems to be done on commercial trunked systems, usually LTR. The local traffic management center/CHP dispatch will have the ability to directly communicate with the FSP tows.