The MSA60 is literally an external disk enclosure. VMware doesn't need to support it. By this I mean, if you were to install Windows, you don't see the MSA60 in your device manager, it doesn't take any sort of driver. You would see the P800 RAID card, and some logical disks connected to it. Imagine opening up a server, running your internal SAS cable through a hole in the back and hanging your disks outside the server. That's pretty much the MSA60.
The P800 IS supported by VMware, so this configuration should work. However, what you don't have within VMware is any interface to actually create a RAID array. And without that, ESXi just sees it as an empty controller. Your server, being a very old G5, won't have the Intelligent Provisioning software modern systems use to get around this problem either. What you should therefore do is:
Download a copy of the HP SmartStart CD
Boot to said CD
Access the Array Controller Utility from there
Create some RAID arrays, and then one or more logical disks. Keep them under 2TB. Even though ESXi 5.1 supports larger, I wouldn't be confident your older hardware would work well with it.
Reboot to ESXi, you should be able to create a datastore.