When we first started opening up our relationship I hadn't realized I was quite as interested in kink as apparently I am. I did raise it with him before I started dating my BF, though, so he did get to "sign off" on it before I started this relationship. He's currently not dating anyone else, but in the past has come home with hickeys. I'm quite amused by them, so no it wasn't a big deal.
As far as just staying covered up after getting bruised, he's asked to be "warned" so as not to be surprised by seeing them. They generally last for at least a week or so and we both normally sleep in the nude so, unfortunately, there's no good way for them to go unnoticed until they disappear.
He's often hesitant to open up about his past abuse, so as much as I agree second-guessing isn't generally a good strategy, I don't want him to feel brow-beaten by me pushing for more information. I think it's enough for me to know they make him uncomfortable and I should try to respect that feeling.