Are 2RS bearings waterproof?
When it comes to radial bearings, the z (usually zz or zzs) denotation identifies a non-contact metal shield, the rs identifies a rubber lip seal.  None of them are waterproof, they are just all different levels of water resistant.  It depends more on operating environment, particularly temperature and bypass pressure.

I would use the zz bearings as replacement as that's what was spec'd originally.