Yes.
I did it for partial backup, since GUIMiner doesn't support normal backup for Phoenix miner.
So, primary miner get around 90 MH/s less speed, but second one can mine at ~400 MH/s if first one fails.
With 11.6 i got the same 440 with single/double miner config.
With 11.7 i'm getting 440 with single and 430-480 (sometimes it jumps to 530+) with two miners on single card.