All the ones I have had for TR's have been Engineers.
I believe the deal with them is they do what ever the TRTO requires them to do (bit of dual so to speak) and then someone from the CAA sits in on them for a day or two and then they get an approval for that paticular TRTO to teach solo. And they also taught the engineering type courses as well.
They were very good at the systems stuff but they usually got a pilot in to do the performance.