EDIT 9/26/2013--- REALTEK DRIVERS ARE NO LONGER A PART OF VSPHERE 5.5!! If you would like to integrate the Realtek Drivers in the ESXi 5.5 ISO, please follow Erik's article - Adding Realtek R8168 Driver to ESXi 5.5.0 ISO
I've had this one backlogged but finally got around to test it out. In my home lab, I am using the Shuttle SH55 that has a Realtek 8111E 1Gb on-board NIC.
Surprisingly enough, I see google keywords coming to my site to look at my homelab using the keywords Realtek and vsphere. With vSphere 4, there were some articles that I highlighted in my home lab post that pointed towards vm-help.com that used a new oem.tgz to inject Realtek drivers into the ESXi installer. The problems with injecting the oem.tgz drivers is that it wasn't native and was prone to problems. When I had a VM using that NIC with vSphere 4.1, pings were lost and things seemed to just disappear. Thus, I made the decision to skip out on using the on-board NIC and continued to use the Intel NICs that are on the HCL.
Well, the good news is that the Realtek NIC is working with vSphere 5 build 381646 (beta build). The bad news is that the vSphere HCL hasn't been updated for vSphere 5 so who knows if it's really supported.
The NIC connects at 1GB with full negotiation without any hacking whatsoever, this is just the basic ESXi install.
Homelabbers can rejoice that you will have an additional NIC available with vSphere 5 that doesn't require any hacking of the oem.tgz and seems to just work native. I'm going to stick with replicating a dual 10GbE environment for now with my dual Intel adapters, but I may just need to use this NIC for some sort of testing in the future.