Since Icinga2 wants mysql and Jasper wants postgres I thought it made sense to install each on its own VM. Has anyone got them working together with Icinga Reports on separate servers?
JasperServer is a standalone tool, and can import any data source and report templates. You can for example measure network traffic and do accounting with the provided data. There's a tool called iRepprt which helps to work with data and reporting views.
In terms of icinga-reports, the package just provides all the reporting views and templates which contain queries against the IDO MySQL backend. Look into the data source configuration in the web frontend, you can safely use an external IP address. That of course means that the database for icinga must be available remotely. Best is to create an additional grant for the jasperserver server und a new read-only user.
You can then have JasperServer running on its own VM, only remote access is 3306 to the IDO database and Icinga server.