Campaign aides are hired more for their skills and knowledge in the domain of running and organizing a political campaign, and not primarily for their political views—provided their views are not so different from those of the candidate that loyalty might be an issue.
However, aren’t high level staffers such as a communications director often given influential posts in the White House after the election. If Thompson had only hired one or two moderate Republican staffers it wouldn’t be such a problem. However, he seems to have a pattern of hiring staff who lean to the left.