When we download the esxi 5.x iso's from vmware download site, is the vanilla version what we usually download.
But exists some custom installable iso's specially designed for vendors like Dell, IBM, Cisco, HP, etc ...
This custom iso's can be downloaded from the same place where we download the vanilla iso. Just select the "Drivers & tools" tab and then "OEM Customized Installer CDs" to obtain it.
What is the difference between the vanilla and custom versions? Well, the custom installable iso's contains some more specific drivers and utilities that permits a tight hardware monitoring of the supported vendor servers. Things like the status of the power supply or the RAID can be now monitored.
Anyway you can also download the vmware esxi 5.x vanilla iso and later apply the bundle from the vendor to be able to monitor the vendor specific hardware.
It's highly unrecommended to use a customized version in a unsupported server.
Just a last comment, the IBM custom iso's aren't available in the vmware download site. The most recent esxi 5.x IBM bundles can be downloaded from here.
HP custom iso's can also be downloaded from here.