A VEH refers to armoured vehicles like Bionix, Terrex, Leopard and the like, >15 tons weight I suppose.
May have to go outfield in recovery vehicles and also have personal wep and veh-mounted wep.
The last I know, maintenance crew heading outfield to support armour unit missions do not receive combat pay, even though they have to bear arms (both personal and veh mounted GPMG) and wear vest etc. Not sure about now, 2 years after though.
Personally speaking from my experiences interacting with the workshop folks during my time as BX operator.