The idea was to fill the raid with the RPG Watch group and use LFM (looking for member) for the remaining slots. As long as e. g. I lead the raid I think Corwin won't have a problem with being in a raid. You could consider the pug characters as hirelings.

Short manning is probably not a good idea.
The raid leader sets the pace and we can easily type in the LFM invitation that we will make a slow paced Shroud to teach a few new to the Shroud. That should keep the elitists from joining.