Yes, he may hear voices. Some can be of his own making while others could come from the thoughts or internal suffering of the other Summoned who have been taken to the altar to undergo the ritual or who are currently rejecting the process. You can coordinate this with other players if you want!

He may also confuse the voices with the whispers that are coming from the Eerie Shrines. One of the shrines is currently unlocked, a second has been cracked open, and they have all started to bleed. They may undergo further changes which you can track here.

He can interpret this to mean anything you wish that will push him in the direction you're seeking. While technically the voice wouldn't be anyone he recognizes, due to his state it would be completely possible for him to mistakenly believe that he's hearing someone meaningful to him and that they're telling him to do something important. You can choose what that is according to what best suits your plans.

You can additionally submit an investigation if you feel he would try to open the shrine, to obtain one of the charms if he has learned about them, or to otherwise force characters to convert or help him investigate the shrines further.