It depends on the kind of veggies you are looking to grow. Most veggies and herbs will grow happily in what you describe. I have about 60 square feet of beds that are at that depth and have been wonderfully producing for years. The main exception would be if you want large root veggies like carrots or beets. You can grow smaller varieties, but not the long/large ones you may be used to. Good luck!

If your native soil isn't rocky, use it. Amend it well with compost before placing the raised bed on top and filling. That way, even though the raised bed will only be 7 inches tall the plants roots will essentially have an unlimited depth of soil to grow in.

Rodney