Running 2 heating elements off one t-stat by having one on a dimmer should work reasonably well. I believe it has to be the on/off kind of t-stat. Something about running something through 2 dimmers doesn't work properly, and the proportional t-stats are just dimmers that are automatically controlled.

However, since it would have to be on on/off t-stat to work properly, I wouldn't want to be using it with a heat lamp. I think that the light turning on & off might be stressful to the snake.