Only cards the same model can SLI/crossfire. e.g. gtx 1080 with a gtx 1080 or an r9 290 with an r9 290x.
In some games with DX12 support for multi gpu's (only Ashes of the Singularity) it could be possible (or 3dmark). However no you cannot play games with two different models of cards in SLI or crossfire.