Probably not. I use Envisage to focus my DSI and I think it grabs the camera and noone else can get it. I have it setup out back now, I'll check it out in a bit.
[edit]
PHD and Envisage both showed the image from the same camera but Envisage poped up and unknown error dialog box after I upped it's exposure time. I guess the camera is like me, it doesn't like more than one person telling it to do different things at the same time

But maybe if you had 2 DSI's you could tell the guide cam to expose for the same time as PHD tells it to expose. Dunno how to get them to tell the camera at the same time though.
These guys might have some toucams ->
http://www.telescopes-astronomy.com.au/ Ring them tomorrow.