Can smelling salts be hazardous to one's health?

Yes,yes, yes! The smelling salt phenomenon is a relatively new fad and there have been deaths associated with its use. Please avoid these other than for taking a bath and then only if you do not have a cutaneous reaction such as contact dermatitis.
Smelling or bath? Let's be clear what we are talking about, because the implications are serious. Smelling salts are simply ammonia-based products used to revive people (frequently boxers). No abuse potential there "bath salts" as they are commonly referred to on the street, are not bath salts at all. That is simply a name given to them. They are a class of very dangerous homemade drugs. Stay away from them please!