Hello,
I did not recieve any feedback till now. For a planned maintenance, I found a procedure (http://www.ivobeerens.nl/2013/08/19/perform-esxi-host-maintenance-on-a-vmware-horizon-view-floating-desktop-pool/) which describes how to perform a planned maintenance.
However, when a host becomes unavailable (maintenance mode, or really unavailable) then it is not possible to edit the pool anymore (error: "Internal view composer error. Contact your administrator").
How should this be handled?