"Vote for us and we'll start talking to Westminster" doesn't seem like a very solid plan to me. Attempting to start negotiations is easy, but then Westminster will simply refuse and point to a decade-old referendum to claim the matter's settled. If they don't have a plan for when Westminster once again refuses then it's just useless posturing.
That said, the tory quotes in that article are a bit unhinged. Voting SNP is bad because they're using your vote as an indication that you support SNP policies, how awful!