You might want to contact a landscape architect.

Where in the PNW? I may know someone to refer you to.

Regardless, this may well be something where it's worth bringing in an engineer who specializes in soil and water issues. Any paver system will fail if the base doesn't properly support it, and your description has my leery of just digging down a foot and rocking out.

I'm just curious, is the goal with the permeable paver a green concern, or are you hoping it will solve the stability issue? I can't speak to the stability issue without seeing the site, but if you're just trying to capture stormwater and take it underground there may be other options. If your sloped driveway is particularly steep you won't get very much water infiltration, so you might be better off pitching the driveway to a bioswale at the downhill side. Just a thought.

I have recently bought a home with a gravel driveway, which is completely foreign to me. I have had ruts as well, as the gravel just pushes out to the sides under the car tires. Under it is clay type soil.
I was told that gravel will always do that and adding more is not the solution. They suggest Crusher Run, which will pack down and harden when dry. It cannot be put on top of the gravel, the gravel has to be removed completely first and the base packed down first. Then later if we choose to pave we can pave over it, but you can not pave over gravel as it is not stable enough.
I hope that helps you.

Gravel drives can't just have gravel, dumped on a path and be expected to work. That's the bubba method. First, the topsoil needs to be removed. Then around 8" of the subsoil, or more, depending on your frost level. Then it all needs to be graded properly. Then you need a base layer of the sharp sand and gravel delivered and packed down. Repeat. Repeat. Then the finish layer of gravel goes over the properly compacted base. Berms and swales need to be constructed along each side to handle water management. A properly constructed gravel drive is not inexpensive.

We successfully constructed a paver driveway on a steep (20% slope), but our sub-base seems like it must have been more stable compared to what you are dealing with. And even then, there was extensive excavation and compaction of base material. There are details that had to be incorporated that make this steep slope construction fairly expensive. You can see a few photos of our project here:

http://www.houzz.com/projects/1595656

Also, check out:

https://www.uni-groupusa.org/PDF/06_Aug_Sloped_Streets.pdf

I like to think we were being fairly green, since almost 1/2 of the pavers we used were reused/recycled.