The heartbeat via the OOB is important in case you have self-fence setupped for a restart.
Unplugging it would cause the server to self-fence, which by default mean all your servers/hosts would reboot.
Make sure your self-fence is configured ok, or just disable HA for the time you do the operation.
Servers will self-fence (that is, power off and restart) in the event
of any heartbeat failure unless any of the following hold true:
-The storage heartbeat is present for all servers but the network has partitioned (so that there are now two groups of servers). In this
case, all of the servers that are members of the largest network
partition stay running, and the servers in the smaller network
partition self-fence. The assumption here is that the network outage
has isolated the VMs, and they ought to be restarted on a server with
working networking. If the network partitions are exactly the same
size, then only one of them will self-fence according to a stable
selection function.
- If the storage heartbeat goes away but the network heartbeat remains, then the servers check to see if they can see all other
servers over the network. If this condition holds true, then the
servers remain running on the assumption that the storage heartbeat
server has gone away. This doesn't compromise VM safety, but any
network glitches will result in fencing, since that would mean both
heartbeats have disappeared.
https://support.citrix.com/article/CTX217735