I don't even think it would be compatible.
You say "non crossfire sli" in your title, two things;
1: Crossfire and SLI are the same but different, one relating to nvidia, one relating to amd/ati.
2: You can't just put another card in with no bridge and expect it to do anything but give you issues. (Unless R9 290/^ that crossfire through the pcie slots)
TLDR;
No i don't think it will work unless i am missing something to do with the cards being the same card in some way.