Its safe at 80 psi for 200*F
That being said. Pex fittings are a bit expensive it would technically be cheaper to go with Silicon hoses for recirculation.
If you are thinking about creating a recirc arm that has a straight flow up and over into the MT, I think thats a cool idea... That being said, I'd rather go with Copper in that place instead, or go full-monty and do a SS piece that can be dissembled and cleaned.