Well, Igor generally makes a contract with the "MC" of the game, and thus starts the series of events that lead to the conclusion of the game. Handling several such characters at once would be a bit more complex. However, he could still do so, though handling a group of people rather than one guy alone means he needs everyone available to tell them information so as to avoid repeating himself.

However, Igor's role need not be exclusive. He could be 'replaced' by the usual wise mystic mentor. Indeed, the biggest reason he should be in this kind of game is, well, because he's been in almost the entire series.

As for evoking the Personas, how would the masks be used? Would a glyph appear on them that we'd have to touch/activate? Or some other special effect?