>"Are competitors able to hire these sites? How can I find out if that is the case?"
If the links LOOK bad, I think you should ask to have them removed / disavow them, whether your competitors built them or not.<
This is the 2nd or 3rd time I have seen this. A site pops up on the WMT links list, with at least 1/2 million links to 1 or more pages on your site, then by the time you get to look at them, they are no longer on the page, so it is impossible to ask the source with specifics to take them down, but they still show in WMT for weeks or more. I can't imagine it is coinicidence.