I do not have a lot of experience drying vegetables, but I can share what I have. First, I haven't had any issues drying store purchased frozen. In fact, frozen corn seemed to turnout well. I literally just dumped the frozen corn right into the dehydrator. It dried and rehydrated just fine.

On beans, I have found that you need to "air" dry beans before adding them to the dehydrator. If you do not, they split and turn to mush when rehydrated.