Does range hood need damper if roof vent already has one?

I posted this in the home repair forum, but I figured maybe this should be the place to seek an answer. During my kitchen remodel I had roughed in 3 1/4X10" duct in the wall that the range hood will exhaust out through the back, go 90 deg up between the wall studs and out through the roof. Now I notice a problem that I overlooked. The damper on the range hood needs at least 3" clearance to open. I do not have 3" clearance because I have a short 90 elbow in the wall.. But my roof vent, made by Broan ( model 634), has a damper in it already. In fact it looks like a better damper than the one on the range hood. It has a weatherstrip seal. So my question is can I remove the range hood damper if the roof vent has one already?
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