is the Cluster enabled for EVC? - in this case you got to consider powering down all the VMs and placing your host in maintenance mode and then drag and drop it on the cluster.
if the cluster is not enabled for EVC, just drag and drop your host in the cluster. No need to power down running VMs.
Narendra Padmani
VCIX6-DCV | VCIX7-CMA | VCI | TOGAF 9 Certified