Legally they can't.

I don't believe your statement above is correct. There are court approved alternatives. As I recall one is to allow each voter to vote for one candidate, all candidates, or any number. Thus minority voters could all cast 7 votes for a minority candidate.

If questioned, their answer is the center was build in anticipation of Summerfield.

I have not heard any commissioner say that. In fact Summerfield wasn't even on the radar when the decision was made some years ago to build the Snow Hill facility. At the time is was built in Show Hill since the location was deemed to be in the geographic center of the county.