Let's Be Frank
My stepdaughter, a Jewish girl, is marrying a very fine Catholic man. My wife and I are looking for a Rabbi in the (withheld) area who will perform the ceremony for them. The groom wishes the actual ceremony to be held jointly with a Catholic priest. The wedding ceremony and the reception are to be held in a hotel so there is no "religious property" involved (ie. not in a church).
I can see that you are sincerely concerned with your step daughter's best interests, and that you want to do the right thing Jewishly, seeing as you want a rabbi to perform the ceremony.
But let me tell you a joke: It was right before Yom Kippur and the Rabbi sees one of his congregants entering a non-kosher restaurant. He could not believe his eyes! As he peers into the window, he sees the man talk to a waiter and sit down. He watches while the man orders lobster and pork and eats it with relish. Unable to contain himself, the Rabbi rushes in and confronts his congregant: "What is the meaning of this?" The man answers, "Rabbi, were you watching the whole time I was eating the unkosher food?" "I saw every bite," says the Rabbi. "Well, then," says the man, "what's the problem? It was under rabbinical supervision!"
While you and I may have differing views regarding intermarriage, I'm sure we agree on the basic principles of honesty and integrity. We both agree that it's wrong and dishonest to create and foster false impressions.
In your search for a Rabbi for this ceremony, you have no doubt discovered that Judaism forbids intermarriage. Therefore, I feel that having a Rabbi at the ceremony fosters the false impression that Judaism allows intermarriage. It's like a type of fraud and a breach of common sincerity. The right thing, the honest thing, is that no Rabbi be at the ceremony.
I have no doubt that your stepdaughter has indeed met a very fine man; but this does not change the Jewish position on the subject. This is not to say that Judaism in any way deprecates or looks down on non-Jews, G-d forbid. Just that G-d has commanded us to be a separate people in order to fulfill our role to be a light to the nations. For our essay regarding intermarriage, go to: http://www.ohrnet.org/ask/ask191.htm#Q1