There are plenty of reserve guys with 9-5 jobs, as others have said they tend to be civil service or defense contractors.

From experience, working at a non-defense affiliated company can be challenging, even with an organization which is supportive because they usually don't know the rules and will do things like charge vacation for AT, etc.

The big problem is that you have to climb the ladder to make the big bucks someday...and there's usually no way you can prove that you didn't get the promotion because you were a reservist. They also may have a legitimate concern that if they elevate you to high things that your military service could be a distraction in the best of times, or a show-stopper if you get MOBed.

If you're going to do more than 2-3 days/month, best stick with civil service or airlines.