The Host Configuration Status for All dashboard has a link for "Hosts with alerts disabled" with a number next to it.
That number seems to be based on a search of "status.enabled = false".

However, when you click on Hosts with alerts disabled to see the list of those hosts, the search shown is "last_report > "61 minutes ago" and status.enabled = false". This search does not include hosts that do not have any reports. In our case, we have 44 hosts with alerts disabled, but the search "last_report > "61 minutes ago" and status.enabled = false" gives 0 hosts.
I guess the best solution would be for the search to only be "status.enabled = false".