I don't think this is call white-hat SEO practice. White Hat is not directly purchase links but they do content + innovative way to get other people links to them. Link purchase is against the Google policy.
I've generally seen it been called white-hat. In my (limited) experience, black-hat is generally used to reference automatic link building, content spinning etc., while white-hat to reference link building through other means that Google will(or can) not automatically penalize.