Imprisoned Vecna and the Planar Ally spell

[cure]

While locked away in Cavitius, could Vecna respond to the casting by one of his clergy on Oerth of the planar ally spell by sending one of his servants forth from Cavitius and out of the Land of Mists? Note that at the end of the spell, the called creature is returned, so it in no way permanently escapes the Demiplane. Would you give the same answer if the caster was in Torvag or in the Core? And would that answer change if the domain border was closed?

Below are a couple of perhaps relevant details from the 2ed Domains of Dread:

"Vecna, like any demigod, is able to grant his priests spells of up to 5th level. He does this as a reward for faithful prayer and devotion to his unholy cause. This ability is not limited by the confines of the Demiplane, so Vecna's priests on Oerth receive their spells just as if their god were not a prisoner of the Mists."

"As a demigod, Vecna can speak to his followers wherever they might be. This power extends even beyond the Misty confines of Ravenloft, enabling Vecna to converse with his minions even on the Quasielemental Plane of Ash and on the world of Oerth."

[Drinnik Shoehorn]

It'd be more likely the caster would receive an ally from the Plane of Ash than pulled from Cavitus.

I forget, though, is Cavitus the domain the same citadel pulled from the Plane of Ash or a replica created by the Mists?

[Cromstar]

It'd be more likely the caster would receive an ally from the Plane of Ash than pulled from Cavitus.

I forget, though, is Cavitus the domain the same citadel pulled from the Plane of Ash or a replica created by the Mists?

According to The Inner Planes the original Cavitus is still found on the Plane of Ash (though its creepy and seems to be empty; apparently his mortal followers have left the place, likely to try and find their missing god). Thus I would say the Cavitus in Ravenloft is a replica created by the Dark Powers.