1.create a vm and attach a rdm disk(-z mode)to it
2.take a snapshot.
3.after that, the rdm disk can't be delete due to the error "Failed - Invalid configuration for device '7'. Cannot remove virtual disk from the virtual machine because it or one of its parent disks is part of a snapshot of the virtual machine."
we know that the rdm disk(-z mode) can't be take snapshot, so in fact it was not include in the snapshot, and i think it can be remove from the vm any time and not affect the data.
esxi version: 6.5d