Is a rheostat like a dimmer?

With two UTHs per cage, I'll run out of outlets real quick! (noo!)

At some point I want to get a helix thermostat. I'm not sure exactly how they work though. If I had one set up with heat tape on a rack, would I have to get a seperate helix for each rack? (I mean if the two racks required different temps) Those things are awful expensive.