Hi RV,
I checked the relative link post for WebI which you posted earlier. For Dashboard the relative path setup would be the same way as explained in that post.
1. To Promote/transport the Dashboards between environments you will need to use LCM ( Promotion management) from CMC and create a job with the dashboards dependent objects. As a best practice it is not preferable to save directly to QA although there is nothing that stops you doing that.
2. To ensure proper communication between dashboards using opendoc just setting up the relative url would be enough as it will pickup the current server info in the runtime.
Thanks!!
Durga