One serious issue is the track records of the writers editing their anthologies. Where they have published anything through other outlets, it's self- or vanity-publishers (Aventine Press and PublishAmerica). Of course, that doesn't imply anything about the quality of their books: they could be excellent works that simply slipped through the cracks of mainstream publishing. But I can't say that this publisher fills me with enthusiasm, based on what I've read.
Ultimately, though, it's the way they propose to remunerate authors that raises the biggest red flag. The "editor's favorite" in some anthologies receives a one-off fee of $50 plus a free copy, the second placed story gets $25 and a free copy, the third placed story gets $10 and a free copy, and the other contributors get no money and no free copy. For other books, nobody gets anything at all. Yet doubtless they will buy copies for themselves, as will their friends and families — which is clearly how Pill Hill Press makes its cash.