Hi,
install the VEIntegration (not the legacy part) onto the Media-Agent.
Install just the DA onto the vcenter and only if you require to backup the vcenter server.
When client cannot be imported, check name resolution on vcenter server and telnet <cell server> 5555. If working try to import the client again. Once imported, import the client as vCenter server in addition.
Now you can create VM backups.
Best regards
Daniel