I have managed at small companies that had reservists. It is a pain to schedule around the reserve obligations. But if I had to fly for the guy or gal and even break duty regs, I did. If he or she is willing to go in harms way, by G@d, I am willing to help him or her get there.
There is NO REASON why any company cannot give a soldier, sailor, or marine the chance to serve. If you TRULY think this is why you were fired, call them on the carpet. I'm sure there are plenty of folks who would give them "wall to wall" counseling.
(and yes, I served enlisted, active and reserve)