My first thought would be "no", as it's supposed to be a spell where no one can detect you. Since True Seeing and See Invisibility don't work against it. Mechanically speaking, I think it's still impossible to cast and take other sorts of actions while under G. Sanc., though I think the engine still allows for interaction with things like doors, which seems to me like a mechanical convenience more than anything.
So my personal thought is that someone under the effects of Greater Sanctuary should not be able to interact with anyone, whether verbally or to pass items or what have you (and yep, I've seen both of these).
I think the visual aspects of Greater Sanctuary (i.e. being able to see a glowing nimbus of a G. Sanc'ed character) are something of a hold-over of Bioware's vision of NWN as a single-player game with some multi-player capabilities.
This of course is my opinion, but since it was Ed who declared G. Sanc as an improved form of Invisibility, I'll let him make the call.
(You're welcome, Ed *winks* )