I have tried that under windows without any luck. The system recognised them, but have not managed to make them both mining, The 290 was mining perfectly, but the second was just sitting on basic frequencies mining almost nothing.
But may it work? Probably yes after a hard playing. Should you do it? No. R series are better with 15.12 (or so) drivers and RX series are better with 17.2 (or so). So I would stick with HD,R in one rig and RX in the second