For your information, not necessarily for your DH yet, there are a couple of (difficult) things I think you should be aware of (sorry if this is a bit much to read just now) as the person closest to him that are specific to the anal rape of a man.
Because of the prostate's position in the anus some men can become erect, feel pleasure and ejaculate during an anal rape. This can obviously make the whole thing very confusing. If he did experience physical sexual pleasure during the rape this does not make him abnormal, it doesn't mean he enjoyed it, wanted it or is gay or any other confusing and self blaming emotion he may be feeling. It makes the recovery more complicated.
The main thing to remember in supporting someone who has been raped is that they are in control of who they talk to, how much or what to talk about.
They need to feel in control of the talking part, but it is beneficial to seek support. So encourage support rather than push to talk. Support services do not require you to say more than you feel you are able. Their aim is to support you to be able to talk more, not push you into anything.
People who have a good support networks and reach out to support services recover more quickly and more comprehensively.
This was not his fault, he is not responsible for the appalling actions of other people and we all believe him and want to support him.