Wedding etiquette...can't have vaccines?

You really are being paranoid about this. I do understand your concern, but a wedding is no different them him being out in the general public. If he goes to church, out to the store, doctor's office, any public situation, he is as likely to come into the situation that you are describing as at a wedding. It is up to him to keep away from general contact with people and be careful. Also up to him if he wants to risk going into any public situation due to his immunity being down. I suggest he talk to his doctor and see how he would address this situation.