I've heard of Ranco before, and I'm told that they're decent. Personally I prefer Herpstat thermostats. This is the one I use: http://www.spyderrobotics.com/products/herpstat.html

About the ZooMed Rheostats and Thermostats... I've never actually used one myself, but I've been told by many people who have used them that they aren't precise, and that they are really not worth the money. I would spend the extra money to get a better quality one. As was mentioned above, you can use them for multiple heating devices, just make sure you monitor them with a thermometer that has a probe, etc.

As long as you make sure that the snake can't actually come into contact with the glass where you have your heater stuck on, and you control the temperature, it should be alright.