Well the paint that most people use to paint the engine cover is rated up to 500 degrees. Not sure whether or not that helps you though.
From my experience though, using plasti dip around hot areas is not a good idea. The heat from my brakes affected the plasti dip on my wheels in some spots and made it a lot harder to get off. I ended up having to use goo gone to dissolve it off, which actually worked very well.
It could turn out very good or very bad, but you won't know until you try. Good thing is if it turns out bad, just take off the engine cover and spray it with goo gone. Then you can just wipe off the plasti dip and have it back to stock
