Right, but a lot of bp.net members have experienced that there are too many risks involved in doing it that way.
1.) with the snake moving around the enclosure, it could get dislodged and end up sitting away from the heat source which would cause the tstat to stay on even if the heat has already reached max.
2.) the probe is "reactive", therefore, it could possibly be that the heat tape is already pouring very high heat before the probe senses the measurement through the enclosure.
So, a lot of people put the probe right on the heat tape outside the enclosure so that it senses the heat right out of the heat source with as little interference as possible.
But, you can weigh pros and cons and just do what you feel is best for your set-up. As long as the temps are ideal for the snake, you're good!