Using the red smite on an enemy and having a team mate kill them will not result in an assist. I saw this happen on Froggen's stream. He smited an enemy 
and his team mate 
killed the enemy a few seconds later, but Froggen didn't get the assist.
Well, I suppose red smite technically doesn't do anything without further attacks, as even the damage reduction is only for the smite holder.
Dunno if it's a bug, tho.
A while ago, I got a kill with kalista by revealing (and only revealing) a champ with my w active while he was taking baron. He died to baron and I got the kill. I don't know if what I found is a bug, but if it is not, then since the red smite has a reveal even if you don't dmg afterwards, you should get an assist.
Basically either reveals are supposed to give assists/kills through execution or not. If they are, what you're talking about is a glitch. If they aren't, what I'm talking about is a glitch.
EDIT: Did some research and found this:
"Champions will not gain assists if they:
ONLY use blind, reveal or attack speed slow, without also contributing in any of the above ways"
So, what happened to me was a bug, and reveals in and of themselves are NOT supposed to give assists.
