I can confirm I have completed a few of these upgrades. I literally just upgraded from Version 6.08 to 6.09 on our VM as an in-place upgrade without any issues and it DID NOT require any firmware updates to the doors. (But I manually set the doors to 'always open' first before carrying out the upgrade as a precaution)
I can also confirm it has never asked me for the licence key in all the years we have had the system (I joined in 2013!)