ESXi 5.1 is not Linux. It is an embedded hypervisor. All ESXi servers are embedded hypervisors. ESX 4.x (but not ESXi 4.x) were based on Red Hat Linux.
You need Data Protector 7.0 with latest patches to support ESXi 5.1.
There is no installation for ESXi 5.1 for Data Protector. Just import ESXi server as VWware ESX(i) server with DP GUI, give login information, and that is it. No Data Protector components should be installed on ESXi server, because Data Protector uses VMware APIs to control ESXi server operations with virtual machines.
Command to import ESXi server is:
omnicc -import_esx HostName -port Port -user UserName -passwd Password -web_root WebRoot -integrated_sec { 0 | 1 }
Example:
omnicc -import_esx esxserver1.domain.local -port 443 -user root -passwd <rootpassword> -web_root /sdk -integrated_sec 0
Now you can create Virtual environment backups.