Military parking spots are actually specified in AFCADs and Aircraft.cfgs.
So I am thorough I will include a quote from jvile on FSDeveloper:
"
MIL_COMBAT comes from the Aircraft SDK and goes in the aircraft.cfg / fltsim.n / atc_parking_types= line. The allowable entires in FSX and FS2004 are:
RAMP
CARGO
GATE
DOCK
MIL_CARGO
MIL_COMBAT
The RAMP_MIL_COMBAT comes from the BGLComp SDk and goes in the TaxiwayParking node properties. The allowable entries in FSX are:
NONE
DOCK_GA
FUEL
GATE_HEAVY
GATE_MEDIUM
GATE_SMALL
RAMP_CARGO
RAMP_GA
RAMP_GA_LARGE
RAMP_GA_MEDIUM
RAMP_GA_SMALL
RAMP_MIL_CARGO
RAMP_MIL_COMBAT
VEHICLE
"
So airports themselves are not specified as military or civilian (apart from the name) but a military airport and in particular it's parking spots can be identified by the above labels. GSX in particular takes info from the parking spot such as size, type of parking (gate or ramp) etc, so it should be able to differentiate with a military parking spot too.
As you all said though, it really needs a developer of this type of addon to be interested in military ground services. It would be cool to have it as an option. FS2Crew are in the process of creating "Ultimate Ground Crew X", maybe someone should ask them (? Bryan) to have a look at it while the product is in development. I'm not sure how that product is going to work, but hopefully it is not restricted to separate aircraft only like FS2Crew, and has an option to be used on a global scale. I do like FS2Crew, and GSX, so to have a product which implements both ideas, and adds military ground services, would be really cool.
Cheers