When one vomits violently enough, it shoots out of the nostrils as well.
From what I can tell, pretty much any poison makes a human vomit if it's strong enough.
SN is toxic. Pretty sure it can constitute as a poison. I mean, part of the ritual is taking antiemetics.
I don't know if snorting poison would cause vomiting, though. I think it would, but I don't know for certain. The human brain is stupid, so it could try vomiting as a nostril cleaning mechanism.
The bigger part of this, however, is that the nostrils are sensitive. Don't know if it's normal - when it's cold and humid enough, my nose will hurt like I've been punched in the face. From the inside!
You're thinking of applying a salt to a membrane. Reading about random shit tells me that it sounds like a fairly bad idea in general, that it'd probably hurt like a mofo.
To conclude, I'm leading towards the "it's a bad idea" side.
Edit: I am in no way a doctor, I'm just a guy who reads lots of random stuff and retains some of the information.