Today it's the first time I heard that there is such a thing as a choir being treated as a fellowship (Interest group with a religious purpose in this case). Thus, that means that not every member in such choir is to be treated as co-workers of our Lord, even brothers and sisters. Otherwise, it would be hypocrisy, wouldn't it?
Obviously, this sort of thing could only happen when people are lazy to preach the Gospel, thereby having the need to adopt some "pretend christians" in order to survive.
Really, this much I know, I cannot having any American Chinese co-workers in my ministry unless some special circumstances which is highly unlikely. I can co-work with them in their ministries, but not the other way around, for I have the responsibility.
Telling a non-Christian: "It's okay that you're not Christian, but you are serving God!" is plainly LYING to the poor soul for selfish church growth benefit.