Do you have to wash frozen vegetables?
Unless you freeze them yourself and don't wash them first, no, you should not need to wash commercially processed frozen vegetables. Part of the process for freezing includes cleaning/trimming preparing the vegetables. Washing is unnecessary.
Info here:

The actual process of freezing a food item varies somewhat depending on what is to be frozen. Peas are the most common frozen vegetable, having virtually replaced fresh peas in the American supermarket. The pea process is typical for many vegetables. A typical process for a frozen entrée follows.
Picking and washing

2 The peas may be picked by hand or automatically. Then, a machine called a viner removes them from their shells. If the processing plant is adjacent to the fields, the peas are carted there. If truck transport is necessary, they are cooled with ice water and then packed in ice for transport. At the plant, the peas are dumped into beds and sprayed with water to remove dust and dirt.