Haku listened to them. Having someone there to trigger memories would certainly be more helpful than trying to sort things out all alone, and with luck, it would help Zetsu. The worst that it would do would probably be nothing.

"I'm a medic," Haku told them both. "If something were to happen, I could probably fix it." It didn't occur to him, however, to use chakra to try and sort out the amnesia. After all, he hadn't had the chance to do so for himself.

If Deidara were to actually mention the Akatsuki and the fact that they were all S-Class nuke-nin, it really wouldn't have bothered Haku. He, too, was a nuke-nin, though from a different village than Deidara, and he assumed Zetsu, too. It would have been a marvelous thought, to know that nuke-nin were coming together to look out for each other.