REC deployer (the part inside of the ISO image) supports Dell and HP but Remote Installer (the Docker image that the Regional Controller instantiates) does not yet, so Dell and HP installs are "1-touch" rather than "0-touch". There are multiple HP and Dell clusters with REC installed on them but they were not installed automatically by the CD system due to the current limitation of Remote Installer support.
Overview of build process
Overview of remote installer and looking at the internals