Is suffixing a UUID derived DICOM UID standard conform?

Absolutely not.

You cannot add anything as a suffix to 2.25 + UUID.

I don't think it's conformant to modify an existing UUID derived UID, and even if it were that it'd be a bad idea to do so. The expectation is that an UID with the 2.25. prefix is followed by a component value that can be coverted to a UUID.

The use of 2.25. + UUID is a registered OID.