Michael,
I just tested this locally and encountered the same thing. When sending to only an alias, the spam checks appear to be skipped. I'm going to create a ticket off this post to track it internally. I'll be demonstrating this behavior to our developers tomorrow during our meeting and will update this thread with more information.
Von See
Technical Support Supervisor
SmarterTools Inc.
(877) 357-6278
www.smartertools.com