Your initial question was to install Oracle Linux on a Mac, for which you received an answer.
Now you want to install it on an HP server? Do you have a system administration background? It seems you are not quite aware of the complexity of tasks that will be necessary for what you are trying to accomplish.
I still think it will be a good idea for you try to install Oracle Linux in Virtualbox on your desktop first to see if you are actually up to the task and can handle the OS, or better get someone with appropriate technical background to do the job. System administration and to set up a server is not a trivial task and requires a certain amount of experience and technical background. You don't learn to swim by dropping into the sea.
I don't not mean to undermine your experiences, but you will have to admit that a HP ProLiant server and Mac OS X server are something completely different. If you have installed Mac OS X server on your iMac, and you want to install and try Oracle Linux on it, then the answer is still the same: Virtualbox. It will also allow you to create networks and even virtual disks, so you can practice with mirroring.
Your other question.... prefer for what? It really depends what for. I wouldn't recommend to run Oracle for production use under Virtualbox on a Mac. For everything else it's great. Performance under Virtualbox is close to native performance on the same machine and depends how many virtual machines you run simultaneously. How the performance compares to an HP server depends on task and hardware and cannot be equally compared.