Answer: I know a Master Gardener who created a demonstration garden using a variety of planting methods, including straw bales. Basically, he removed some of the straw from the top center, replaced it with a mix of soil and plenty of compost. Then he planted his seeds, kept the soil moist until germination, and so on, just as if they were in the garden.
However, this was in Phoenix, and since the bales sat up on top of the soil without protection, there was a problem with them drying out. Since the plant roots can't spread very far to seek moisture and nutrients, you'd have to keep an eye on moisture levels and any sign of deficiency, such as yellowing leaves. You should be able to try any type of vegetable (except perhaps corn), since the bale is just a big container.
I think it's a good idea to try some type of raised bed rather than fight the rock. Since you seem interested in alternatives, I have another suggestion for you, called garbage bag gardening. The name says it all, but basically the container is a heavy-duty plastic bag! There's a web site with more information at http://ctaz.com/~dclupper/. Good luck!
Q&A Library Searching Tips