A purpose built combat pusher would have a few advantages in mid airs and crashing. The prop wouldn't be as likely to slice up an opponent's wing, or break your engine mount out of your fuselage if you hit the ground.

However, here are some disavantages:

1) need for pusher props. harder to find

2) launch technique may need mods. With a conventional "tractor" config, just point up and let go. Most electric wings are first thrown and then powered on. Can't do this with gas.

3) goofy exhaust direction. Mostly cosmetic, but still a consideration. Tuned pipes and mufflers would point forward.

4) pusher configs sometimes suffer cooling problems -- especially in cowled scale applications. You don't have the high pressure blast over the cylinder like a tractor config.