I think you don't need a group. In my configuration, DSPAM does not deliver any
mail but is only used to classify a mail. Other software such as amavis and exim
are responsible to transport the resulting email to the appropriate places.
This is entirely possible without using groups.
Groups can be useful to share a common DSPAM profile or the have a basic
out-of-the-box filtering for new users (merged group) if all users have a
similar "spam" definition.
For the single spam alias I think embedding the MySQL UID in the signature will
solve that.
Executive summary: You don't need groups for a virtual setup.
fs
