Host migration without downtime

All,

We have 3 exchange servers hosted on 3 ESXi hosts in vCenter_A environment.

We have another ESXi hosts in other vCenter_B environment.

So there are 2 different vCenter environments.

We need to merge vCenter_A hosts into vCenter_B environment.

Following below steps will have any Exchange downtime?

--> From vCenter_A, "Disconnect" ESXi host, then click "Remove"

--> Connect this ESXi host (i.e. "Add host") into vCenter_B environment

Or there will be no downtime for Exchange servers.

Or best way to do is shutdown and then "Remove" --> "Add" the hosts?

Please suggest.

Thanks,

Mihir