You can use propane to heat water for your site, and you can use it to heat sauces/glazes. You can also use a propane weed burner to light your charcoal before your meat goes on.
You cannot use a propane device to cook your competition meat. So you could not put a glaze on the meat and then use a small torch to carmelize it on to the meat. Also, you could not use propane to heat water to boil your ribs if you were so inclined.
If you need more clarification, please submit a question under the judges section and they can give a more "official" information.