No, I'm certain they knew people would pick it up (how could they not; it's some pretty blatant stuff). And they did it more in tribute and reverence than anything else (and I'm glad they did, because it made my filmgoing experience that much more enjoyable, because I caught most of the inside jokes and references - and there are A LOT of them).

My point is that a good sector of the filmgoing audience doesn't realize that, because they've never heard of "Dreamgirls" in the first place, and EXPECT a Motown biopic when they hear the words "loosley based upon the Supremes". To be honest, the movie exists somewhere between "loosely" based and "inspired by". Perhaps the key was that they should have made sure all publicity said "inspired by" (which gives the impression that it's still a fictional work) and not "based upon" (which gives the impression that it might be a biopic).