I actually saw some (military contractor or related manufacturing) companies which continue to pay full salary (plus the employee gets whatever active duty salary and allowances). These companies also donated stuff like satellite links to their employee's unit so they could have Internet access.

I would probably do this at my company (even outside of defense), purely to be more attractive to NG/Reserves candidates -- a lot of them have great additional experience and training which is paid for by the government, and especially if they value their military career and security clearance, are unlikely to get involved in anything untoward.