As long as you keep the heat away from your glue, you should be fine. A number of people use heat to "temper" the belly of their bow to reduce the probability of set, and to add a few pounds of draw weight. But they normally do it using a heat gun and they normally put the bow in slight reflex during the process.
You probably could do it using fire but you'd need to be pretty careful. Also if you do decide to do it, make sure that you don't flex the bow for a week or so afterwards. The heat will dry it out to an unsafe level, and it needs to re-acclimatize before you stress it.