First workaround, Cluster Validation was good but SQL installer still complained
Setup /SkipRules=Cluster_VerifyForErrors /Action=AddNode
Second Workaround is actuall a MS Bug, where I had to comment out the pre-saved license key in the installer folder and entered it manually instead
Basically go to \x64 folder and modify the Defaultsetup.ini file to comment out the serial number (and paste it in during install)
;SQLSERVER2008 Configuration File[SQLSERVER2008];PID="XXXXXXXXXXXXX"