First off, I don't really think you can equate acceptance of using a condom for oral to the acceptance of using a dental dam for oral. Why? Because one is more common than others. As has been mentioned on here before by active swingers, dental dams are rarely seen.
When you first discussed your safe-sex only policy with them did you specifically discuss dental dams? If not, it is very logical that the thought never crossed her mind and she assumed you just meant oral sex on the guys. It is much more common for disease to be spread in that way than by a guy performing oral on a woman.
Please don't think I'm saying this was your fault, just that maybe there was some miscommunication here from the beginning and what you thought was made clear wasn't.
Now if on the other hand you had made the dental damn concept clear up front when you discussed safe -sex. Then I think it was very unreasonable of this woman to get as upset as she did, and you would be correct if she wanted oral without protection her husband could have provided.
Question: Do you require the other guys to use a dental damn when performing oral on you? Just curious.
Julie
http://www.swingersboard.com