Unofficial support for VersionPress. Note that VersionPress is currently not being developed: https://github.com/versionpress/versionpress/issues/1481.
Generic question: I'm trying to set up development -> staging -> master areas.
Can I issue a wp vp pull against another repository that is neither a clone nor a master of my current repository?
you can synchronize only sites which were created by cloning. We are calling them instances, please see docs. It should always start with one source site (with VersionPress manually activated) and then you can create staging (testing) site, use remote workflow (see examples), etc.
Generic question: I'm trying to set up development -> staging -> master areas. Can I issue a wp vp pull against another repository that is neither a clone nor a master of my current repository?