As of today the actual algorithm for SD0026 rule excludes any non-numeric --ORRES and ‘* Ratio’ --TEST records from the validation of --ORRESU value. Therefore example from page 118 of SEND IG is OK. Do you have any particular issue with this check for PM domain?
I think, that you brought another very good point about validation rule development, that a check assignment shoulld be the same level of importance as the check itself.
In your example --ORRES variable has a non-numeric value. The SD0026 check should skip such records and no warnings are expected. That approach has been implemented a while ago in previous versions of the validator.
We just tested with the latest version of config.xml and I can confirm that SD0026 is no longer reported for PM with non-numeric --ORRES, which is great (definitively better than disabling the rule for this particular domain).