This question is ultimately dependant on your network design and risk tolerance.
A few points of note.
If your hosts have uplinks to to 2 separate switches, they will reboot alternately and therefore the hosts and VM's should see minimal impact.
This assumes your hypervisor pathing is set up correctly.
If you have the VM's storage traffic (iSCSI, NFS etc) going over the network. Most hypervisors can handle a small delay in connectivity to the VM storage, but won't handle a larger outage time. It's always a more enjoyable experience to shutdown critical VM's prior and bring them up again later than to have to recover corrupt VM's.