I own both foam and resin heads these days. Wearing something on top of a head should work just fine provided it's not too tight. As for the ears, I think the best bet would be to have the thing made to be compatible with the head by having slots for the ears, since at least on all my heads they wouldn't be able to support anything heavy without bending.
In short, I think the best bet would be to have armor made to fit the head or a head made to fit with the armor. Not really sure what else can be done, but then again I'm no crafter so chances are someone somewhere have got some nice trick up their sleeve. I guess asking both the person who's going to be making the armor and the person who's making the suit if it'd be possible to have the things made to work together would be the best way to know for sure.
Not really sure I understood the question right, but I assumed you were asking about wearing something on a head.