I can not solve this problem.
There are several servers with ESXi 5 (the same issue with ESX 4). VM's contain oracle linux and various oracle software.
Periodically hang the VM with error
That's probably a question about VMware and your hardware rather than Oracle Linux. You seem to be running out of physical RAM, hence the OOM killer in Linux activates to sacrifice processes in order to free up memory for the system when all else fails.
Swap is not a substitute for RAM. It helps to page the memory of idle processes to disk to free up conventional memory. However, the kernel needs physical real memory to be able to manage memory pages and also to manage the swap space. If your system runs out of low memory it will eventually crash, but OOM will kill processes before that happens as a last resort to stay alive. Memory exhaustion can even happen if you have a lot of memory installed but use a 32-bit kernel and do not use kernel hugepages, resulting in very large memory page tables and bad performance.