I've configured the Splunk Add-on for Java Management Extensions (http://docs.splunk.com/Documentation/AddOns/latest/JMX/About) and got it working against a Tomcat JVM.
I could search JVM metrics only through search (index=main sourcetype=jmx), but there is no UI dashboards for this.
When will Splunk ship the dashboard please?
As above... we're also working on add-ons that use JMX to do more specific tasks, like IBM WAS and other application servers. These come with prebuilt panels that you can add to dashboards.
The point of this add-on is not actually to have any UI dashboards but rather to gather data and perform proper tagging/extractions so that the data is readily consumed in the dashboards and searches of other apps. From the documentation page that you linked:
The idea of a Common Information Model is to enable a point of indirection so that add-ons like this one, can map data into the CIM, and other apps, including but not limited to the two premium apps listed in the documentation quoted above, can build queries based only on the CIM to drive visualizations, alerts and other search results.
Now if you have a use case not covered by the CIM, you can still build your own searches and dashboards. You may consider building your own data model, but you don't have to depending on your use case. There is information included in the search tutorial on How to create a basic dashboard, along with in depth reference on Dashboards and Visualizations, and many more resources on building your own provided by Splunk and the community.