Plenty of airline/GA/biz pilots in the reserves - though not in flying jobs. I know of two airline pilots who double up in RMR, three in TA and one in RNR, all in non-flying jobs. One RMR has done two tours with RM - one to Iraq and one to Afghanistan.
Biggest problem is finding an airline employer in these stretched days who is prepared to give time off. Sqeezyjet is one of the best.