I would keep your eye on the wound. I probably would not take him by the sound of it but for further confirmation of what to do a picture will help if you can get one.
If they are caged together I would seperate them immediately. Chameleon's have hollow bones just like birds. A veiled chameleon can quite easily break the other ones bone/s/ in a single bite. They tend to go for the opponents jaw or leg. You may have gotten a little lucky he did not get a hold of his jaw if this is the actual case.
A burn is possible. Seems more likely for the burn to have occured on his casque or top part of his back near the head. Still could happen on the tail. Check your basking temperature. With veileds I think it is important to not let them have a branch that goes directly under the basking bulb or at least tell there is enough distance for the temperature to drop signifigantly. You also have to watch the gaps in branches in this general area. If they can get a hold of two branches they may still strech out directly under the bulb. They do not seem to feel the casque very well or the spikes on their back and this is why burns tend to pop up there. Again this is just what I have normally seen with veileds and burns. Situational things and variables can lead to burns any where.
If your not sure about what the basking temperature should be, give the age or your best guess so someone can stir you in the right direction.