Yes, but you have to drill many holes in it first. You need to get your hands on a hammer drill, and a 1/2" masonry drill bit(figure out how deep the pad is first!). Drill holes every foot or so. Shouldn't be to bad, just wear a dust mask.

Hi
Maybe you could use one of those "roof gardening" techniques?? Saw this dicussed at length on a garden show.
Google that and see what you come up with. Obviously they didn't drill holes in it yet allowed the roof to drain. believe it was on the PBS Victory garden show.
gary

I'd suggest astro turf to make your life easy.
Yes you could do this, but 6" isn't going to be enough if you aren't willing to break the concrete. i'd say at least 12-18 inches would be needed and then you will need to water a lot because it's going to dry out quick.

does the patio slope away from the house?
you will need to build something to retain the soil, but
i would also suggest lining it with landscape fabric to
keep soil from seeping out of the 'planter', bring the fabric all the way up the sides. i would also put in a 2-3 inch layer of crushed stone under the soil to improve drainage and then use something like potting soil to grow in
also some sort of drainage piping to lead the water off to where you want it to go might help if you don't break the concrete. think of it as a very shallow container garden