Just upgraded ESXi from 5.5 to 6.0 on my HP DL380 G5 with the "HP Custom Image". Thought it'd work better than the "vanilla" (generic) image.
The install went well. But from time to time, it kept giving me the purple screen (system crash), usually 10 - 20 minutes after the VMs boot up.
A search led me to the URL http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2085921
But it didn't fix my problem.
Finally, I decided to "upgrade" with a generic image - overwrite the HP custom version with a generic version.
The installer gave me warning on the RAID controller. P400 controller was "not supported" by 6.0 any more. I ignored and continue. The install completed successfully.
Now I'm living happily ever after. :)