That depends on how sophisticated you want your storage to be. You can achieve basic HA storage by using NFS exports, that are backed by a HA setup. The pros are: easy to setup, likely easy to configure on the HA storage
The cons are: no thin-cloning of guests and disks (all copy operations take the real time to complete), more latencies with file access
If you want to go with a more powerful setup, you'd export iSCSI targets, or even FcOE targets, should your infrastructure provide those, and use MPIO to those targets. That would enable you to create OCFS2 repositories, which support spare files, reflinks (clones) and better latency.
I opted for the latter and went with iSCSI/MPIO. The targets are hosted on an ASM cluster, which is backed with btier-enabled storage.
Note, that Oracle treats the OVM servers as "appliances" and you will have to live with what the system comes with. Installing any 3rd party software on the OVM servers is not supported by Oracle, nor is it feasable, since you will likely run into a number compatibility issue, since OVM is based on a highly patched RHEL5.