Well, I can see how a drop of whiskey rubbed into the gums would actually work with teething, although I think orajel works better and is a bit more acceptable. But how is whiskey supposed to help with congestion? How much? It sounds like they're recommending enough to knock the child out, which sounds extremely dangerous, and even moreso with congestion. It sounds like an absolute recipe for disaster, in fact.
Fwiw, we were always able to deal with congestion with the aspirator, or aspirator and vaporizer going in the room. I don't even know what meds you could give an infant for congestion. I don't think there is anything.