So, question is, 1996 Camry overheated and cracked the head. I am replacing the head and it's already milled or zeroed, whatever you want to call it. What I want to know is do I have to get the block milled and zeroed as well?

Or, is the milling the of head enough to ensure I wont have problems?

Have the block checked for being flat. It is not likely to be a problem for warping, but it's easy and cheap to test before you put on the head.