I can confirm the camo dudes do not use Pro-Voice. I have been out there with "DSD" and it doesn't recognize the signal. Further, I have played the audio to LMR dealers and they swear it is AEGIS DES. I have photographed the camo dudes radio and they use a MRK as far as I can tell.
In my last visit to the range (November 2011), the only trunk signals you decode are from the DOE NTS (aka N2S2). But posts indicate Nellis is on a new system. To be honest, what is posted isn't terribly good, perhaps due to the system being in a state of flux.
Your best best is simply listening to VHF/UHF milair. I provided a good list in my previous post. Bandscanning gets you the VHF Groom frequencies very easily. There are ground units that use the air frequencies, but you need to be on TIkaboo Peak to hear them.
I ran into someone who got a ride with Steve Medlin at Bald Mountain. He was there when Steve used his radio to contact the base to cross the border. This person isn't into scanning, so I got no details on the radio. But given the cost of those trunking radio systems, I would bet they have an analog back door for Steve and made the sheriffs department.
This is the photo that has what I believe to be a GE MRK next to the window:
http://www.lazygranch.com/images/bald/spongedude.jpg
I could make a Facebook page for many of the camo dudes since I have photographed enough of them, but they get fired if their identity is revealed.
Note the dudes also carry a receiver for the Qualtron EMIDs, so potentially that is the radio seen in the window.
As far as I know, WSI does not do security for Groom. Previously it was EG&G, but EG&G no longer exists. The powers that be have compartmentalized the security contracts, giving the NTS, Groom, and the TTR different vendors. The TTR security is done by the Washington Group.