Is it a good idea to pass a oven range hood exit duct in the roofs' ventilator?
Seems like a bad idea. If it is sealed so that only air from the range hood goes through it you have eliminated an attic vent.
If it is just kinda pointed at the attic vent you will be introducing moist greasy air into the attic space.
Also the chance of a kitchen fire getting into the attic greatly increases with any option other than a termination cap designed for and exclusively used for range hood.
Use a smooth hard metal duct to connect the hood to the termination cap.