What would be some veggies to grow in a rock garden?

If you can provide 6 to 8 hours of sunlight per day you can plant anything you like.

You can grow potatoes as they grow shallow and you pile peat moss or straw on top of them. The best thing is you do not have to go out and buy seed potatoes, you can take your favorite store potatoes and wait till little eyes form on them and then cut the potato in sections with 3 eyes per section. Then plant it shallow. I put a plastic straw or you could use a stick at each planting about 3 feet apart. As they grow keep covering the most of the vine with more moss or straw keep doing that until late summer and you will see flowers and then the vines die. When they die you can start digging carefully around your sticks and moving the straw and you will have many potatoes that are great.

Depends on the amount of sun the area receives. Sunny area I would plant strawberries. Summer squash, look for the type that works in containers. Watermelons. Tomatoes. Now is a good time to get seed catalogs and read on the requirements of different veggies. Good luck and have fun.

Tomato - Onion - Carrot - Beetroot - Cabbage - Salad stuff

You probably don't want rocks around the vegetables. The rocks will collect heat and heat the soil up. If you can leave open the top of the tiers, and just edge them in rocks it would be fine and you can plant whatever veggies you want. The rocks also would be a hassle with planting each year, as you would have to move the rocks out to plant. I am assuming that the area gets lots of sun.