Sure the frostier the plants the better for hash making. Hash is just the trichs, heated and pressed. Really pure hash is almost all trichs, the green looking skuff hash is IMO lower quality, it's the vegitative matter that gives it the green color.

I'm not surprised that you don't find sativas as medically helpful with pain management. I was under the impression (although not a med user myself so I could be wrong) that heavier indicas helped ease pain more. Sativas would probably be better for depression with their cerebral high. If the medicine you have works well for you, I'd just keep that in rotation and try out some other indica dominant tasty plants. Perhaps Yumboldt or Bubbleberry.