I have lost count of the number of times that we have looked at a 'star' and discovered that it was actually a binary... There was one recent laser run where the observers were needing solitary stars, They had a target list of likely candidates and several targets in a row turned out to be binary- previous observations did not have the resolution to tell that they were binary.

I would think, given the scales involved, that even a binary system would not show much in the way of dark matter effects. Binary systems are separated by a fraction of a light year- the dark matter effects seen so far are galactic in scale- 100's of thousands of light years...