Finally ownCloud can be installed via plugin in OpenMediaVault. Currently it is in beta status, thus any tips, bugfixes or other suggestions are welcome to improve the ownCloud plugin.
After installation the ownCloud GUI is available via http(s)://xxx.xxx.xxx.xxx/owncloud. Note, if you access the ownCloud GUI the first time you’re automatically logged in as ‘admin’. The default password is set to ‘openmediavault’.