Q. Can I mix Configuration Levels in a Windows Server 2016 Failover Cluster?
A. Like Windows Server 2012 R2 it is supported, although not recommended, to mix Server Core and Server with a Desktop in a single cluster. It is even possible to add Nano Server into the mixed configuration environment however once again this is not recommended. Your cluster should be running the same OS, same configuration level, same storage stack (cards, firmware, drivers etc) same networking hardware. Any deviation from that consistency should only be on a temporary basis as part of migration scenarios and not the long term state.