Joseph,
Why are you assuming the coming on to the dance floor thing is a non-Jewish custom? Have you been to non-Jewish weddings where they did this?
I assume it happens at Jewish weddings because the Chosson and Kallah separate from everyone else in the Yichud room and then come back and rejoin the wedding. But at non-Jewish weddings the bride and groom don’t leave the wedding party and then return, they are there the whole time.