Aside from the article Mal quoted, I saw nothing on the web to suggest that pistachios are toxic for dogs (It could be that the presence of loud abdominal rumbling that made the vet concerned, in conjunction with the nuts...who knows. But who posts emergency vet questions on the internet?!) The ones I saw mentioned most often were macadamias and walnuts, although one site said "In fact most nuts are not good for a dogs health since their high phosporus content is said to lead to bladder stones." None of this seems terribly scientific. "Is said to..."? What kind of medical evidence is that?
Anyhow, just err on the side of caution. Peanuts are probably pretty safe, since peanut butter is a common ingredient in dog treats, so if he really likes salty treats, go with those, but sparingly. Since he's a toy dog, and probably pretty small, it doesn't take much of anything to poison him or throw off his dietary balance. Nuts are pretty high in fats, and dogs need a good omega 3 : omega 6 ratio in their diet to keep their skin and coat healthy.
Here's a list of other stuff dogs shouldn't eat:
http://ezinearticles.com/?Grapes,-Nu...Avoid&id=20315