I think you missed my point. I am trying to launch sa-learn from root. Two reasons, one I don't want spamd to have shell access, and two I am writing a script.
No, -u does not work with sa-learn. It is not in the docs, and never has been.
However, you can add the --dbpath parameter to sa-learn's command line to work on a specific bayes DB... However, you may need to chown it back to being owned by spamd when you are done.