Hi, please take a look at section "About Tarball- and Yum-Deployed Hadoop Distributions" and "Configure a Yum-Deployed Hadoop Distribution" on page 14 of VMware BDE Admin and User Guide, it describes how to add a distro.
In VMware BDE, CDH4, MapR and Pivotal HD are treated as Yum-Deployed Hadoop Distribution, so please follow "Configure a Yum-Deployed Hadoop Distribution" to add CDH4 distro. This includes mirroring the official CDH4 yum repo and a little copy/paste work in /opt/serengeti/www/distros/manifest. There is a sample for CDH4 distro configuration in /opt/serengeti/www/distros/manifest.sample.
config-distro.rb is used to configure a Tarball-Deployed Hadoop Distribution (e.g. Apache Hadoop, CDH3, Greenplum, Hortonworks, etc).
-Jesse Hu @VMware