I have plesk 7 running just great with the SA addon for spam. It sees the spam just fine but does not re-tag the subject to *** SPAM ***
I have SA running fine on other servers that don't run plesk. Here is my local.cf file
# How many hits before a message is considered spam.
# Whether to change the subject of suspected spam
# Text to prepend to subject if rewrite_subject is used
# Encapsulate spam in an attachment
# Use terse version of the spam report
# Enable the Bayes system