There are a couple threads on this, I think one was in the medical school forum. I think the consensus was that it is possible, but generally not a good idea for most people and that if you do attempt it, you should wait until you've been in med school for a few months and have a good idea what the workload is and how much time you'll need to spend studying and to pick something that allows some flexibility.
I think it also depends on your options and cost/benefit ratio. ie. working 10 hrs a week for 10 bux an hour is not likely to be worth the time sacrifice and you're probably better of studying/working to get a good residency. However, for some people who have the ability to make 30-40 bux an hour, working 10 hrs a week would be great. I just went to a non-trad med school info session by a local program and one guy worked 2 X 12 hr shifts a month as a clinical lab scientist. I'd guess he's at about 25-30 bux an hour for that. I've seen a few previous nurses, NP's, PA's that still pick up shifts.