HBase & Mahout - Using HBase as a Datastore/source for Mahout - Classification
It's not directly possible, no. You can revive this old implementation, and dust it off and probably make it work without much trouble. It was indeed removed to slim down and focus the project.
You can of course also look at exporting your data, in some form, and adding it to a representation or store that is directly supported.
Generally speaking, you can use HBase with Mahout by virtue of the fact that Mahout uses Hadoop (mostly) and Hadoop can use HBase. That's not quite the situation here; there's a more direct integration point here, that has been deprecated.