It heavily depends on the virtual switch used
With standard switch this is kinda easier:
1. Change the DRS on the old cluster to partially automated
2. Disconnect the host from old vcenter
3. Connect the host to the new vcenter as standalone
4. Move it to the destination cluster
5. Repeat with other hosts
With distributed switch it is bit more complicated.
Your new vcenter won't recognize distributed switch details you had on the old vcenter
Migration steps should be more like this:
1. Change the DRS on the old cluster to partially automated
2. Disconnect the host from old vcenter
3. Connect the host to the new vcenter as standalone
4. Connect the host to the new distributed switch -> do this really carefully and slow
a) connect the host and first uplink
b) do the vmkernel migration to the correct portgroups
c) do the VM network migration to the correct portgroups
d) connect second uplink
5. Move it to the destination cluster
6. Repeat with other hosts
7. On the old vcenter remove the migrated hosts from the old distributed switch
Of course all these things should be done with the assumption that new vcenter does not have issues with network connectivity to the esxi hosts
Moreover if you'd like to avoid the risk of any mishap during this switchover, then since vsphere 6.5 u2 you can do cross vcenter vmotion without issues.
There is even fling for that, that makes whole migration easier.
