Does anyone know anything about gardening?

You can lay tiles over Ecobase, they just won't stay put.

A point worth knowing about shingle (as opposed to the decorative stuff) is that a lot of it comes from a saline environment so will not be conducive to plant health. Naturally, weeds will colonise it and flourish regardless.

Any loose stone surface will gain fertile soil from rotting leaves, dust or whatever within very few years. It will grow weeds whether you put down an underlay or not.

I'm not sure. I guess you might be able to. As Colin said, without doing something you'd probably get movement. It would add to the cost and I'm not sure what benefit there is. Where they work well is as a concrete slab substitute.

Or do you mean can you lay Ecobase over tiles.