I've dehydrated peas, green beans, okra and carrots all from frozen foods and had success with each.  However, I heat them up in a microwave before they go on the dehydrator, a step that supposedly keeps the veggies from spoiling.  In years past, I started the food prep a couple of months before my trips and never had any problems.

This year I decided to try to simplify the food prep and ordered from Harmony House as Beefman suggested above.  Since I don't have a garden readily producing homegrown veggies, this alternative saved me time, and was cheaper than most other options.  I'll let you know how the end product tastes in my trip report, but their veggies look fine, and they were easy to order online.