The trunking system used at Nellis AFB (Motorola Type II UHF) uses APCO25 along with the TSA at McCarran Airport. Hoover Dam Police also uses P25 along with the Bur. of Reclamation on their repeater network that serves the Boulder City area and Arizona.
A good source for this and just about any other scanner related information for Southern Nevada can be found in the Southern Nevada Scanner Book which I understand can be found at Amateur Electronic Supply in LV or at Radio World in Boulder City. I highly recommend the book for anyone seriously interested in monitor radio listening.