I tried the dk-22 with the fm2 standard eye piece (no eyecup) and it works fine. The dk-22 is a tight fit and does not stick out as far as the eyepiece that comes as standard with the 600, so I don't think there is a risk of it falling off.
The fm2 eyepiece is rubber coated, so would be fine with glasses (AFAIK, all the ones in that range are, so no problem if you need one of the corrective ones).
Personally, I prefer the eyepiece that the 600 came with, but this was just an experiment so no drama there. I felt that the view wasn't quite so good with the above combo, though there were no significant issues with seeing the whole frame.
If you want the eyecup as well, then you need to order the dk-3