are they any benefits using MCS hardware over IBM or HP own servers?
I do prefer using Cisco branded MCS servers over the non-MCS versions primarily due to support issues. If you are having a problem that may be server related and open a TAC case you won't be referred to the 3rd party (HP or IBM) for resolution. There is "ownership" within the case with MCS boxes. I have also found that the Hardware testing/verification phase of the install goes much smoother with the Cisco branded servers. We do know that both MCS and non-MCS boxes are supported for installs, so this is just my preference :)
Supported Cisco Unified Communications Manager Releases by Server
Hope this helps!