Here’s a collection of location where you can find ESXi 4.x and ESXi 5.x customized by vendors, loaded with drivers for certain hardware types.
The first place is a „Custom ISOs” tab on Download VMware vSphere site and available vendors are Cisco, NEC, Fujitsu, Hitachi and HP. Not every vendor for every version but for ESXi 5.x you will probably find what you need.
Contrary to what is said here, I do not see ISOs for DELL servers on VMware site. Following the instructions from the site mentioned above, we can pretty easily find custom ISOs by DELL under Enterprise Solutions on Drivers & Downloads site for each system.
As for IBM ISOs on VMware site, I can find only ESXi 4.0 U1 so if you want more you need to go to this IBM site and select a proper ESXi version (all are included).