It only seems to be the coach and BoD who said anything about it...
you can see as he runs into that tackle o-gara takes a knock on the head from a prop running back with his arms over his head and appears to slump to the floor rather than commit fully to contact, and considering he was convulsing (which isn't that common with a choking, if my memory serves me correctly) it seems that it is almost certainly not the case.
Also - if you were going to try and put ogara out of the game, you wouldn't do it with 20 seconds to go, since it's pointless...