I got this problem too, OMV 2.2.
Tried first to install through omv-extras. Got the java error.
The following packages have unmet dependencies:
openmediavault-subsonic : Depends: openjdk-8-jre but it is not installable or
openjdk-7-jre but it is not going to be installed or
openjdk-6-jre but it is not going to be installed
Tried through SSH as root to install java.. 8, 7, headless, jre, jdk. No go.
Tried to install tzdata-java, which said i needed tzdata, which is already installed.