As far as I know ONMS doesn't have an overview of all monitored services.
There is only the search windows at the starting page.

Principle it could look like the availability view on the starting page.
A list of all known services. If you click on one, you get a list of nodes which have this service. Atm I don't have an idea how to handle polled and non polled services.
Maybe the outage and availability column like in the availability view could be informative.

The longer I think about it, this idea could be more than one feature. The overview list itself, to see which nodes have this service, should be found in the info menu.
And maybe some kind of availability view based on services. Could be found in menu status or maybe optional for the starting page.

What about a graphs? A donut graph which shows the amount of services? In numbers and percentage.