Under normal operating temperatures, you should be OK...but if you get the engine a little too lean and hot, it can melt into the plastic a bit...BTDT.

Edit: I'm talking about the gray glass filled nylon type, like the Kraft-Hayes or GP mounts. Some of the mounts I've seen that come with ARFs seem to be more plastic or have more plastic in them and are more flexable, and might not be as temperature resistant, so...?