Onboard NICs are Intel, but not the normal ones supported by the Proset drivers. I'll have to get back to you with the exact number but I think it's E1's. They do support ESXi and the HP app allows teaming/failover under Windows 2008R2.
A general brain dump:
One thing to keep in mind is that the onboard RAID controller handles the drive bays and the two SATA ports. However, it only supports two logical arrays, not including CD/DVD drives. So if, like me, you were planning on an OS drive on SATA and two RAID1 arrays in the bays, you can't. Limited to RAID 0/1 and AFAIK hotplug requires both an additional license and a replacement bay.
Write caching is enabled through the HP RAID manager software, so I'm not sure how you would enable it under ESXi. The RAID controller (in RAID mode at least) isn't part of the standard Windows 2008R2 driver set, so you'll either need to have them on a USB stick or use the HP prep tool to install.
iLO3 remote power/remote is limited without purchasing an additional license, but it will allow control until Windows boots (so you can get into the BIOS OK).
Power usage was surprisingly low, around 80 watts under load with a single disk.
The onboard GFX are, as expected, pretty poor, over RDP it flys. The HP software is all very nice, there's a lot of it. I'd advise downloading and using the BIOS update service pack disk which will do the MB BIOS, RAID, NIC etc. for you.
It's pretty quiet out the box. Adding a PCI-E card seems to have turned up the lower bay fan, but still not bad at all.