VMware ESX / ESXi 4 does work out of the box on the HP Proliant ML110 G5. I know, I'm using ML110's with ESX 4. However, I still see posts like this http://communities.vmware.com/thread/163029 were people have problems with this ML110 and ESX 4 and even ESX 3 combination.
Now, if you look at the link to VMware Communities, you will notice in one of the screen shots attached that the CPU is a 1.8GHz Dual Core. The ML110 G5 comes in more than one CPU, so beware that when you decide to get one of these HP Proliant ML110 G5 for running ESX 4, make sure you get one with the Intel Xeon 3065 CPU that runs at 2.3GHz. The reason is because not all Intel CPU's shipped with the ML110 supports Intel VT, and this is a requirement for ESX 4.
Now I know you're probably saying: "The guy in the post is not using ESX 4." My point is simple: It doesn't matter what version of ESX the post refers to. If you want ESX 4 to run on the ML110, make sure you have the correct processor.

Ok, so we've looked at installing VMware ESX 3.5 on the ML110 G5. Now it's time to look at installing ESXi 3.5 Installable on the HP Proliant ML110 G5.
This should all work well, providing that you have the correct storage controller settings specified in the BIOS setup of the server.
To install ESXi 3.5 on the ML110 G5, follow these easy steps:

We know now that VMware ESX Server 3.5 works well with the HP Proliant ML110 G5. So, I thought I'd try running it on the HP Proliant ML115 G5. This however did not go as well a I thought it would.The integrated NIC in both the ML110 and ML115 is not supported, that I knew, so I installed an Intel Pro1000 GT NIC in the ML115. This card is supported so I was able to install VMware ESX 3.5 on the ML115 with no problems at all.
However, when the server booted up and started loading the VMKernel modules... that was where it all went horribly wrong. The server could not mount the root partition!!! Read on, because there is a fix to this problem.
@ChrisBeckett @pmilano1 So I caved and replaced my USB-C docking station with a DisplayLink-enabled docking station… https://t.co/HPARaZVAYo