Awesome. Although I think the 500r you ordered can control two devices, but at the same temp levels. You will need the cool UTH to be set lower than the warm UTH, and I don't think you can do that with that thermostat.
A lamp dimmer will work O.K for a UTH set quite low, the fluctuations are O.K at 80-85 degrees, where as if you used a dimmer on the warm UTH, fluctuations of 90-95 would be a little too high for my comfort level.