The fact that CRIs are not also FIs is irrelevant, they are still authorised instructors. Consider yourself as a trainee on an IR course conducted by an IRI who is not an FI - would you have difficulty with how to log that flying?
From FCL.010: 'Dual instruction time' means flight time or instrument ground time during which a person is receiving flight instruction from a properly authorised instructor.
Consequently, unless the AOC Operations Manual says otherwise, training flights conducted by CRIs in SP aeroplanes should be logged by the trainee as Dual.