My husband said that Simon Jacobson publicized a letter he got from a black woman who lived in Crown Heights. The woman was greeted by the Rebbe every day and she made it a point to be there in order to be greeted. One day, she asked the Rebbe whether she could ask him something. The Rebbe agreed and she said that her children were grown and she didn't know what to do next.
The Rebbe told her to move to Florida and join the church there which she did and was so grateful for the advice.
The point my husband was bringing out was that according to this story, the Rebbe encouraged her to be a part of the church, so maybe this proves (if the story is accurate) that shituf is not a problem for a ben-Noach.
