I've just seen some that use the HID projectors bolted straight on without a housing. This makes sense as long as they're weatherproof!?
That would depend on the type of projectors they've used. But as you stated they bolted on without a housing, that would make them NOT waterproof.
There are projector lamps available that are waterproof but whether they have HID in them is a different matter.
My mate has a set of projector lights but it's just led's in them, they are quite bright but I wouldn't like to use them to see the road ahead.