Depends on the situation, the wife, and the cuck... Wives that want to see their husband suck cock are sweet - often, they have "scripted" in their head what they want to see, and will direct the action.
From the dominant's perspective, if the cuck is reasonably HWP and not an ogre, and the wife is into it, I can get hard and enjoy the experience. Especially if she "trains" him and shares my cock with him.
If the cuck is a great while whale, gross, or otherwise not worthy of sex, not so much. Those are the kind that I demand excuse themselves, and leave the room, if the wife wants fucked.