I wouldn't. Even if you washed all the salt off, which would require soaking rinsing and repeating several times, they could be a big nitrogen draw. Use a smaller pot or fill bottom with something else some people use packing peanuts. Lava rock mulch is cheap by volume and lightweight

As to a nitrogen draw by decomposition, I'd have to suspect that nut shells wouldn't do that. It's very hard to compost them unless you grind them up first. The point about salt, however, is a good one. Just washing off the surface salt isn't enough. The shells are going to have absorbed a lot of salt, and they'll release it slowly in a moist mix. I'm not sure if it's done like this for pistachios, but for salted peanuts the salting process is actually done by pulling a vacuum on them, which sucks brine both inside the shell and into the shell itself.