Of course they can drop pollen in veg. Preflowers of the cultivar types are well known for this and now and then I pollinate my girls in veg for a limited seed test utilizing male preflower pollen. Those female preflowers add up on a nice bushy cut in veg.
The more pristine and natural a line is the more you ll see less of this disposition. It is most noted among the early finishing IBL lines and the others faster short season types.. I have African stock that will never throw any pollen unless in bloom for 3 weeks min