I have a few customer who have deployed Oracle 10g on my ESX cluster.
In general, make sure to avoid using the balloon driver at all cost.
The memory reservation must match the memory allocation for success.
Carve a dedicated lun for oracle data and another for logs.
My opinion, Oracle is bumpy ride on ESX, but I have to admit that it does work, especially if it's given a dedicated esx in your cluster. That said, why not just give dedicated hardware to RHEL in the first place.
good luck