Bengalsfan,
Yes, you can take as much time off as you need from the regional to pursue your military flying. And the bonus is you still accrue seniority at the regional while doing it! The regional (or any company for that matter) is obligated to allow military to pursue their duties as needed.
We have many people at my company who take a week off every month and do the guard/reserve thing.
I would definately say that for you, it would be the best of both worlds.