Is it possible to migrate xDB data from existing Sitecore 8.2 to a fresh Sitecore 9.x instance using the xDB Data Migration tool? I mean if I install a fresh Sitecore 9.x instance (not upgraded one), can I migrate the analytics data from 8.2 via the migration too having only the Mongo Collection database, or it requires some other data from existing solution (e.g. some data from Master and so on)?
It should be possible.
The only one thing I see in the xDB Data Migration tool where some data from Master are needed. It's a profile data. To migrate profile score facet properly you need to have all these items under
/sitecore/system/Marketing Control Panel/Profiles.