What is the version and patch level of the ALM/QC product you are using? Have you contacted HP Support? If you are blocked from updating only the one table this could be either a defect or intentional functionality.
(Opinions and information contained in this post are wholly my own and do not reflect the opinions of my employer.)
This turned out to be a restriction imposed on the Command object (updating the audit tables). Just as it can be done directly in Site Admin, the Site Admin API (SAClient) has a method RunQuery that is not subject to that restriction. Problem solved.