I apologize that I do not have a direct answer for you. However, I have a question and some comments, though:
Are you planning on using ASM for storage management or a more traditional Linux style file system?
Regarding the shared location:
1) If you have availabilty of a iSCSI SAN, you could create a new volume, install a Software iSCSI initiator, and share that way.
2) You can create a .vmdk (Virtual Disk) that points to a raw partition, called an RDM (Raw Device Mapping). This device will either pass all disk operations directly to a raw device (perhaps a unformatted volume on a SAN somewhere) or act as a middle man which will provide some more VMware expected .vmdk functionality (snapshotting, cloning, etc...). See the following link for some more information, though:http://vmzare.wordpress.com/2007/02/19/vmware-raw-device-mappingrdm/
The physical RDM option may be your best option. However, I am not too sure how it would work in a DRS/VMotion environment.
Also, you are going to need to create a seperate Virtual Network for the heartbeat communications. Ideally this is an isolated network with only the hosts participating in the RAC connected.
So, that is my two cents on the situation. Hopefully it helps point you in the right direction.
~Bill