My friend put an M7 in his Vader 7 string. I can't remember if he had to trim the tabs a bit or bend them, but I think so. I can try to confirm that for you.
Yeah I don't know why they make their tabs like that. You can still install you just have to trim them down a bit in size. I had a hard time getting my M7 in my RGD2127. I should have shaved the tabs a bit, but I just kind of forced it in.