Microsoft System Center Virtual Machine Manager

Do we really need it with only 1 host server

Depends. You need SCVMM to do P2V migration and it does provide a nice overview of the status of the VM's and better snapshotting functionality, but no, you don't (and it's much, much cheaper if you choose not to use it)

can it be installed on the Hyper-v host

Yes, unless you're running Hyper-V Core (the free edition)

What about the Microsoft Data Protection Manager

I found that DPM had some serious shortcomings (we switched back to Backup Exec, thank God for technet subscriptions), but they weren't related to SCVMM. To do D2D you can't use removable disks (!!), but yes, it can be the same host as Hyper-V and SCVMM (same caveat applies, it can't be installed on Hyper-V Core)