Calebinfloroda, Ive heard SDAs that believe like that I think its called British Israelites or something similar but Ive never met anyone that believes it.
WingCommander the SDAs do mix with other churches they have in Australia the 'Womens day of prayer' where women from every denomination gather together I don't know what they do maybe they just pray. The womens day of prayer is held in a different denomination every year. Ive been to many meetings in other churches that were advertised in the SDA church.
As I said before there are 700 independent ministries that many teach against the official SDA church in doctrine and are supported financially by ordinary members.