Bonus points if it can factor in the default recruitment system.

You could tap into ALiVE's event system and (with a % chance or w/e condition) spawn a vehicle or create a vehicle recruitment loop everytime a recruitment HQ is created. Can post more later (on mobile atm)

Alrightly, whipped up a template to use.

http://pastebin.com/VVP4CkXq

You must register this file as a function and then change the

#define MAINCLASS Sample_fnc_vehicleReinforcements

line to whatever you name the function.

Then, in some other script file (initServer.sqf will do), call the creation of the object and give it the asymmetric commander's faction

Sample_vehicleReinforcementsHandler = [nil,"create"] call Sample_fnc_vehicleReinforcements;
[Sample_vehicleReinforcementsHandler,"faction", "Asymmetric_faction_here"] call Sample_fnc_vehicleReinforcements;

Now the object is created and will start being referred to when the asymmetric commander reserves a location (how recruitment HQ's are created). The only section of code that you need to edit is the

case "OPCOM_Reserve"

switch case.

I have already put a little bit of helpful information there regarding the objective that get's passed to the operation call. Insert whatever code you wish to use after //-- INSERT CODE HERE

Make sure all of this is done on the server, and not on clients.