I believe we already occasionally transplant tissue from other species. Still, the concern is certainly warranted, particularly with endocrinal molecules. Maybe overstated, but still...
Since the human embryonic lines are (thankfully) limited and unsuccessful, I don’t think it’s too large an inference to be somewhat skeptical. Still, any hope is still hope, particularly to loved ones watching one succumb to the disease.
Postscript: many older diabetics still use animal-source insulin, though the Pharms are phasing out its production.