The air  coming through dryer vents may be contaminated with various hazardous chemicals, including carcinogens.

In general its probably best not to use scented laundry detergent or softeners. The ingredients of scents and fragrances do not have to be listed legally.  And there are not currently any regulations concerning dryer vent  emissions.  Even if it would turn out that they are totally harmless – why take a chance?  Scented laundry products are not something you really need and they add no value to your life.