I had the idea that the main reason behind chosing Harmony was that Google wanted to allow propietary development on Android, and that was not possible using OpenJDK class library, as it is GPL's (not LGPL'd).
Also, a pair of notes: Isn't JavaME in version 6, just like JavaSE?
And Harmony is not the base for Dalvik. Dalvik is the VM, Harmony a class library. As a result, Harmony is code that, together with application code, runs on Dalvik.