"the hell out of something" is a slang way of exaggerating about something that has been done properly or sometimes if it was overdone. So they hammered the hell out of the wall = they hammered it too much. They dug the hell out of the garden = they dug it a lot.

They surely did not love that poor guy. I think it expresses that they tortured the guy to obtain information; I am not really sure.

If you hammered the hell out of someone, it means you beat them up physically.