When editing a server, the Address textbox should be greyed out since the address isn't changeable. This is true both when the server is in Up mode and in Maintenance mode.
The host address field will be disabled(greyed out) while editing a host. The field will not be disabled in the host is in InstallFailed status. Patch : http://gerrit.ovirt.org/#/c/5309/
Checked on rhsc-2.0.techpreview1-0.scratch.