No, there is no integration like that provided. However, some of what you're looking for could be scripted manually and done with Q2A plugins. You can also use SSO to allow users of the wiki to log in to Q2A.
Searching across a completely different set of tables is not possible at all and I would assume is way outside the scope of Q2A.
I don't know exactly how and what you want to cross-link but you could do another plugin that takes the title or tags from a Q2A question and finds relevant links on the wiki.
You could make a plugin that takes the content of a question from Q2A and inserts it into your wiki database, then optionally hides the original question.