In an improvised soul-friendship oath ceremony, Rudi drinks from the cup that the Goddess offers to the Lord, then Mathilda drinks from the cup that Mary held for her son. I would think that this ceremony is valid in either tradition?
I attended a hand-fast where my Wiccan neighbor, who was not being hand-fasted, merely attending and participating, was surprised to find himself without any prior warning reading aloud a prayer invoking the Lord Jesus! Of course, the somewhat inept celebrant had failed to make clear from the outset that, since the bride was Christian, her deity had to be invoked as well. The first rule of effective ceremonial is no surprises.
Multi-faith events are meaningful if everyone knows what they are doing in the first place. At a ceremony for peace in the Catholic Cathedral, Lancaster, there was a sharing of scriptures from the Veda in Sanskrit, the Torah in Hebrew, John's Gospel in English and the Koran in Arabic.