There is a product for x86 only (Oracle VM for x86), this runs on Linux and is based upon Zen. It uses an OVM manager and OVM servers.
There is another product for Sparc (Oracle VM for sparc), this runs on the T-series servers and are based on the Sun Logical domains (ldoms) software. There is a command line interface (there is a gui but I believe the GUI doesn't support ZFS filesystems).
So, if you are using the T-series servers then I'm assuming you are using Oracle VM for sparc. You can choose to create ldoms with the ldm command line interface or by using Ops Center. Pros and cons: I find the cli is sometimes easier to use to configure t ldoms than trying to do the same in Ops Center. Definately more work to configure via Ops Center. On the other hand, once you've configured the ldoms with Ops center you have more management options via ops center. However, it's very much an either or situation, iow, if you used the cli to configure the ldoms you can't later on decide to manage them with full functionality via ops center (last time I checked you had to recreate the ldoms from scratch since you have to start with a baremetal provision of the control domain for the ldoms via ops center)