Having flown a number of fans, Eurocopter and not, it is my belief that there is no such thing as "fenestron stall" as a phenomenon unique to fans. The fan on the older Gazelles was too small and had too little thrust. It didn't stall, it just didn't have enough poop in some situations. It was fixed by changing it to add more max thrust.
The Comanche and S76 Fantail demonstrator could fly at 80 knots sideward, and point independent of the direction of travel up to well over 100 knots. No fenestron stall there. Or better yet, "it flew pretty well, for a fenestron".
I would bet the comments of the experienced 135 drivers below ("flew for 8 years and never touched the pedal stops") tell the story, build a tail with enough thrust, and you will have no problems.