I couldn't import my P2 Adobe export into Avid Xpress HD 5.6. It came up with an odd error that the audio was longer than the video. I needed a workaround to consolidate a spanned P2 card to work in Avid.
I could scrub the Adobe P2 clip in Avid and it looked the way it was supposed to, but it wouldn't play. I've been meaning to post a question about it..... but the best way to find out if you lose any quality is to do it, and look at it...zoom way in....
The DVCPro HD codec is pretty robust, designed to hold up over multiple generations. Although I've never tested it myself, from what I read my guess is that the P2 media will hold up far better than HDV or DV would quality wise.
Whether it works or not in other applications is a different matter.