Actually, I haven't worked with any I think. Maybe just one, don't remember. But I'm a keyboardplayer myself. The thing with submixes is, you'll just have one fader to ride. The mix in between the different sounds is our own thing, but in the end you need to ride just one fader. And the keyboardplayer will tend to compensate the different volumes in between patches himself. As where you don't have a submix, he cannot compensate anything...
It would give problems if he's making a submix and his monitors are bad... But that would be about the same without a submix since he'll try and compensate it with playing harder. (I'm also a saxplayer, horns die if the monitors suck.... oh my...)
