How soon are you building this?
If its going to be a few weeks, I can try to do an experiment for you. I have the watercooling system here, but I need to get another HS/F and a pelt.
About the ground. A lot of people will pull the 3rd prong out of a plug to fit it in a 2 prong timer (the cheap kind) DO NOT DO THIS WITH A POWERSUPPLY AND PELTS!! Basically, if there is a short, instead of catching fire, the electricity gets sent back to the plub and it trips a breaker. Pelts draw as much power as the power supply can possibly give it, which in turn heats the power supply up, and with a cheap power supply in very rare cases it can melt the wires and short out (not a problem if its grounded)
Same thing with your lights, especially if you have them inside your terrarium, they should be grounded.
I did actually use the cheap timers and pull the grounds off my surge protecter to use it, but I spliced the 2 grounds together and hooked em to a bare plug so its still grounded to the house. (I didn't check the timer, and didnt feel like going back to home depot)