I'm in the reserves and was told to expect unpaid leave if called to active duty. I think that's a fair trade. I'm in a training command squadron so my chances of being deployed are next to nil.
I do know of a C-5 guy that got called up and subsequently "quit" Cathay. IT'S RUMOR ONLY, but I hear he didn't tell Cathay the whole truth about his involvement with the reserves and in response Cathay basically told him it would be "difficult" for him if he remained in the company after being deployed.
Bottom line, tell them what's up if you plan on staying in the reserves and, I believe, they will work with you.
If you do try to fight the system, they will bite you back, right or wrong. Is it worth the fight? If your answer is "no" then don't apply to Cathay. If your answer is "yes" don't apply thinking everything will be just ducky if you get called up.