With all due respect to SFU dean of graduate studies, I don't think they necessarily have the final say as to what work experience is or is not accepted for immigration purposes. I checked that particular section of OP6C (Section 6.3), and nowhere is it mentioned that non-taxable income is not accepted.
Just because you receive a research funding in lump sum at the beginning of the term, it DOES NOT mean that you are not paid to conduct your research activities. As long as your funding (taxable or non-taxable) is dispersed specifically to remunerate your research activities, your RA should be considered PAID work experience. Now, if your scholarship is for something else not related to your research (such as to waive international differential fee), then obviously you cannot claim this as your research compensation. But if it is a research funding, it should be fine.
The most important part is to document your TA/RA duties and lead statement, and also the number of hours (which may be a challenge if your research funding is non-taxable). Hard, but doable.