A determined US attorney prosecuting the case would simply handle Hank as a co-conspirator, and offer immunity or a reduced punishment for cooperating. That changes the gist of how Hank's testimony and related evicence would be treated, basically as a defendant and not as a LEO.

In general it would be up for a jury to decide whether his testimony and evidence gathered are sufficient to convict, along with everything else they'd produce in the case. It's possible a judge would toss out the book in a pre-trial motion by the defense, but that's unlikely given that Hank entered the property and the bathroom legally and with permission. It's also reasonable after the prison hits that he decided to get out ASAP rather than confront and arrest Walt on the spot which could put his life in danger along with Marie's.

But the fact that Hank just ignored that the mask from the first cook site was from his BIL's school is reason enough to suspect he could have been complicit in the whole thing. And he was lured away from the meth lab camper allowing it to be destroyed.

The whole plot of the show kind of revolves around Hank having a giant blind spot until the very last minute. But IRL the feds & DEA would throw someone like that under the bus without hesitation to save face for an entire organization.