Horrible situation for you to be in. Do you actually have any concerns that your OH is or has cheated on you? Do you think he takes drugs when he's with them?
Generally I disagree with ultimatums as it gives no room/option for discussion and I think it often compels the person being given the ultimatum to pick the worst option out of spite.
Given what you've said, I totally understand why you wouldn't want your OH to hang about with these two folk (I'd hate it too). But I think he does have a point in that if you don't think he's cheating or taking drugs or doing anything that 'breaks' the rules of your relationship, he should be allowed to pick his own friends.
I understand your anger regarding your hospital visit, but to be fair to him, if he was already out and smashed out of his face, he wouldn't be any good to you, and at 14 weeks I think a lot of partners think its safe for them to go drinking (they're not expecting problems). Obviously I'm saying this based on my understanding that when he went out you were okay, and the hospital visit was a suprise, if he knew and then went out - that's a whole other kettle of fish.
If I was you, I would withdraw the ultimatum (I really really don't think they serve any purpose) and try and open discussions with him again. Maybe you'll never like these people, but maybe you have to accept that he does want to spend time with them, the key thing is to ensure that he is still committed to you and your child. Once the baby arrives his opportunities for 'painting the town red' will diminish greatly, he may well just be making the most of it while he can.
On the other hand, if, deep down, you've decided you no longer want to be in a relationship with him, and you've partly given him the ultimatum hoping he'll make that decision for you, then maybe you need to think carefully about what you actually want, and if you no longer want him, tell him.
Sorry, if its not what you want to hear, and I hope you get a resolution soon.