As far as being a professor and another job, that's a no. Not because I want to be mean, but because being a professor is a lot more responsibility than many other jobs on the site, and also because if they're in multiple maskings, it will cause glitches in the office and becomes more trouble than its worth. They can always just say they do the other profession they're interested in as a hobby on the side.
When it comes to other jobs, here's my two cents: being in a specific masking, i.e. Artist or Astronomer constitutes a full-time job that you are paid for via the bank. I know there are some glitches lately, but that is the plan. To try to add in another group is highly illogical because it's nearly impossible to work two full-time jobs in the real world, and on top of that, the way the bank works, you would be getting paid for both jobs when you're most likely only fulfilling the responsibilities of one (healers, for example, are supposed to be posting in their hospital or clinic, taking care of patients, which usually leaves very little time for say, studying stars as an astronomer). Dark wizards are the exception to the rule, however, as you do not get paid for being evil or causing mayhem. So I *do* think it's okay to have that as one's secondary group on top of a different career group.
In short, no I don't think it's okay to have two career groups, but that's not to say you can't have a job and rp out doing other things as a hobby, that's the beauty of character development. 
Edited by Prof. Stella Giordano, 28 June 2014 - 09:19 PM.
Edited to include dark wizards