ok, i have added an entry "moderator" to the database and it also shows up in the edit usergroups panel, but it doesn't seem to have an effect, i.e. the users assigned to that usergroup still don't have moderator rights. I also tried with other WP roles such as editor, author etc., as I think it doesn't matter (?) if a user is a moderator in WP but can be assigned moderator rights in PP (basically). Moderators global rights are turned on.
Seems as if WP doesn't come with a dedicated "moderator" role, but with "editor". I have defined a moderator role though through a membership plugin (s2member) which is accepted by WP.
What would also help is if I was able to manually assign users as moderators to a category, but that also doesn't work.