Mixing physical and nested Hyper-V hosts in a 2016 cluster

Q. Can I mix Hyper-V servers that are nested VMs with Hyper-V servers on bare-metal in a cluster?

A. Failover Clustering does not distinguish between the types of nodes added to a cluster so that alone would not block the cluster being supported. If you run validation and it passed then the cluster would be supported but obviously you are likely to get a lot of warnings because the network and storage stacks would certainly be different and although this may pass it is not really suited for production purposes.