Maybe I'm dumb, but I haven't found anything regarding helmets for cosplay? I was thinking of doing a cosplay suit this year that requires a helmet with a semi-transparent (it's color tinted) face shield. But, if that's against Gen Con policy (as I know some venues have a no mask/concealed facw policy) I'll rethink what I plan to do. My face would technically be seen a liiiiiittle bit because of the semi-transparent part on the front, but a helmet's a helmet. 

Nope, there's no policy against helmets that cover your face.

For example, people have been wearing Star Wars stormtrooper uniforms at GenCon for years, and there haven't been any problems.