@Dak
We should probably start thinking about providing a virtual package for JRE/JDK.

In the scope of "Instant Coffee" I had started to package Java applications for Maemo and upload these to the extras repository.
http://talk.maemo.org/showthread.php?t=51871
https://garage.maemo.org/projects/instant-coffee

I packaged versions of the OpenJDK build via IcedTea6 (the package is called "icedtea6") which can also be found in extras.

Currently I am referring to "icedtea6" as a dependency for all Java packages.
The benefit of providing a virtual package would be that Java applications can depend on the virtual package rather than the "real" packages like your "mmjre" or "icedtea6".
This would give the users the freedom to choose which Java implementation they want to use and makes it easier for people creating packages for Java applications.

As far as I know this is done by adding some "Provides" entry to the control file of the "real" packages.
Though, I am really no expert when it comes to packaging applications for Maemo and don't know if or how this will work using the autobuilder.
Generally, I'd suggest that we try to do something similar to the way Java is packaged for Debian