I've seen some of the western hat/safety helmet hybrids. I think that in order to get the hat totally covering the helmet, it makes the hat too big. That is why they look silly
Eventers and long distance riders use the riding helmets, whether they ride english or western and they look okay.
I wear one when I'm riding with my western saddle and even if my fellow riders snigger, I just smile and continue. I don't care what they think, I'm protecting my brain!