There could be a nuance that it is possible that Michigan does not consider legacy in evaluating applicants to score them for potential admission, but does consider legacy when making an individual yield prediction (which includes other factors as well, such as stronger students being less likely to yield than students reaching for admission). Even if maximizing yield is not the goal, predicting yield is necessary to admit the number needed to fill, but not overfill, the class.
So your own status as a legacy or not would not affect your admission, but if you are at the margin of admission based on admission reading scoring or evaluation, how many legacies there are among those rated more highly in admission reading could affect whether there is enough space for you to be admitted when getting to the margin of admission.