I have often wondered about using lab incubators, too. We have several at the university where I work that aren't being used. However, all the ones that we do use here keep the environment inside the incubator VERY VERY dry. My only concern would be drying out of the eggs. But you could put a tub of water in the bottom or something to keep humidity up. I say go for it! Especially if it's free.

As others have said, you could always just put some flexwatt on a t-stat in there.