I was a fully ASE certified mechanic at an Oldsmobile dealership. Courses taught by General Motors specifically stated you should NOT use cruise control on wet roads. I don't think this applies to modern traction control though.
I can’t help it GM is run by lawyers...I do know that those same lawyers hadn’t affected the ability of me to use my cruise in the rain (although they could have, easily) - with or without traction control engaged.