Annnnnd, Yes they could use State Police freqs. If, you can get you hand on one of DPS's little yellow books that the Troops have, that have the names of teh troopers and unit numbers in them, you can find out the US Marshalls unit number allocations. I have not seen one since the early-mid 90's.
Any unit number on a DPS freq above, I think ??? 700 - 1000 is a Fed. State Fire Marshalls in 1700 series, DOT...I do not remember...and....State Forresters is in there somewheres to.
Later.......FF-Medic !!!!!