I went to lunch with the dean at my school this past week, and there was another student there with us. She (the other incoming 1L) mentioned at one point that she would be working part time during the year, and the dean essentially said "Stop talking... lalalalala"
In other words, as long as you don't make a big deal about it, and keep it on the DL, it's not going to cause any problems with the school. But, I personally think it's a bad idea. Like the last poster said, why would you want to risk sabotaging yourself just for a little extra money that, in the long run, will make very little difference in your life?