Yes, Rheostats are dimmers that can control the output of electricity to what you are using. (I clumped it in there with thermostats, sorry)

I wouls suggest getting a thermostat instead of a rheostat, considering the fact that if you don't have a way to determine what the temps are for the UTH, what would be the purpose of adjusting the temps?

Get a thermostat for the UTH, and a rheostat for the lamp.