Now, this question is very interesting here. Not only can you steam frozen vegetables but this actually may be the preferred option. The primary reason is that when you do so frozen, you are able to better retain the nutrients that your body craves and needs. These machines do a better job of retaining nutrients anyway and when you steam your veggies frozen, it enhances it even further. Also, this can increase the flavor of the end result. That is certainly not a bad thing at all that is for sure.