Well Ann Bell is the one to ask this. She sent me pollen during the winter that she had dried and frozen. I am using it now. And I don't know what you mean by "Dry" pollen. Do you mean pollen that is open and fluffy?
I take mine off the plant when it is fluffy and put in those little vials. I leave the lid open over night to dry, then close it the next morning and freeze it. Ann taught me to make several vials of the same pollen and use one til it is gone, then open another one. I was just cramming it all into one or two containers, then if it got bad or not viable anymore, I lost it all. I take it out and let it warm up in the room then go out. I actually put it back in the freezer, but Ann does it differenly. She has these pill containers for the days of the week. She dumps pollen from one container into the pill container and labels them as to what is what. When she gets done pollinating she puts the pill containers into the fridge. She says the pollen will last about a week this way in the fridge. Then she dumps out the old pollen and starts using a fresh batch.
I hope this answers some questions, I am certainly NO expert on this. As soon as I get a lot blooming out there, I always prefer to use fresh pollen that is blooming that day.
Dot