I don’t think we’ve ever had anyone professing beliefs outside of Western traditions—mainly the three Abrahamic traditions—one Hindu, one Buddhist, and various irreligious categories. We have had, however, one Scientologist member of Congress named Salvador “Sonny” Bono, so we have had at least one occultist.
In all honesty, I’m more interested in when the first open believer of a New Age tradition, European pagan, or Native American animist gets into noticeable office. I believe the only major candidate that ran recently from those categories is interfaith spiritualist Marianne Williamson for a House seat and President as of late. It’s kind of surprising to me that a major nonchristian person of an indigenous faith hasn’t ran yet in the Southwest already.
We probably will never have a Baha’i politician, as the faith bars people from getting involved in government and politics.
Former New York City council member Dan Holloran was a heathen (Germanic neopaganism).