It's better than nothing, but honestly, if you have the money I'd go ahead and buy a thermostat. They're SO much easier to maintain, you don't have to cheack the temps as often. (Cheapest I've found are on http://www.reptilebasics.com/ plus, the guy who runs Reptile Basics is so nice, he'll nswer any questions you e-mail him)
I'm no expert, so I'll just tell you what I've been told. If you're going to go with a lamp dimmer, connect the UTH by following the directions as if you were connecting the dimmer to a lamp. You should purchase a temp gun, you can find them fairly cheap and they tend to be the most accurate. Plus, with a temp gun you can check the temp directly on the glass under the bedding as well as on top of the bedding, with a digital probe you'd have to move it around and it's just a pain in the ass.