Yes, if you have 2 heat sources you need 2 thermostats. I think belly heat + RHP on both sides would overwhelm a divided T8 though. I use just 11" wide FlexWatt in mine and even when the house drops to 70*F it's ok.

I have three of the T8's with sliding doors, and other enclosures have drop-down doors. I find the drop doors easier to manage. Also I've found with the sliding doors that the left side of my T8 stack, which has the door on the inside track, stays a lot more humid than the right side. So, I run my juvenile BRB's in there, and my juvenile Dumeril's boas on the other side, since both species have the same heat requirements but the BRB's need higher humidity.