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It depends on the site and the privledges given the person who is administrating the site.
Administrating a site does not give you automatic privledges afforded the site owner who originally set the site (Xoops or otherwise) up.
So an administrator can say they don't have database privledges and be telling the truth.
I have database privledges on my site because I set it up, so I can look at or read any pm's. No body else can... even if allowed to administrate my site.
Maybe that will help you answer your question.
BS
Sidenote: Yes, the SITE OWNER can, in most cases, if they know how, (and many don't) trace any action preformed on their server.