Sean Connery has always been credited as Tack in official literature, as early as the 60s I believe.
Animator Andreas Wessel-Therhorn floated the idea that maybe Connery was never actually recorded, but that the voice was just intended to be Connery upon completion.
I can't be sure either way, but I like to believe that Connery recorded his one line very early on.
Ed E. Carroll is credited as The Thief in Fred Calvert's version, in which some annoying gasping and yelping from The Thief is clearly audible. Someone pointed out that similar vocal effects are in the workprint, but much softer in the mix. I was convinced, with some prodding, to include Carroll in the credits for the workprint version.
I'm not sure about his actual presence in the workprint, as Thief vocals could have been done by anyone at any time.
I will say that due to the Recobbled Cut mixing different audio sources, you do hear Carroll there.