@willplaice: the SATA controllers/drives in the MacMinis are being recognized in ESXi. That is also true for the new Late 2012 series. You can use them as local storage and/or to install ESXi onto. Howerver, the MacMinis don't have an internal RAID controller and ESXi does not support softRAID (softRAID0 support would'n hurt, by the way). So you have no redundancy on DAS in a MacMini.
I never tried installing ESXi on SD card. But I guess it would work. On ESXi hosts with DAS we simply install ESXi onto it. Diskless "workers" in a cluster are being booted from USB key. You may PXE boot them also, but not with Mac, because Apple uses netboot instead of PXE and I believe there's no VMware support for that yet.
For NAS/SAN you can use the biuiltin Gigabit NIC and/or attach several Thunderbolt devices, such as the Apple Gigabit Ethernet Adapter, which will give you NIC failover for just 25 bucks, the Sonnet 10GbE adapter or several FC HBAs. I only have experience with the Apple GbE and it works well. We do larger Mac installations with MacPro and regular Intel 10GbE NICs.
Keep in mind, that the MacMini only has ONE Thunderbolt port. It is also shared with the Display Port, so you can't attach the cheap miniDP-to-VGA adapter and have to use the HDMI port. That often is an issue with KVM switches in a rack or server farm. However, there are HDMI-to-VGA adapters available for +50 bucks.
For HW-RAID you can use any Thundebolt-to-PCIe Adapter (Sonnet would be my first choice) with any supported RAID controller (I would pick LSI here). But I would not recomend that design, because you end up with a dozen of external boxes and any cabeling problem will crash your system severely. If you add up all the price tags, you almost end up at the level of a MacPro, where you can easily put all those cards into its PCIe slots.
But beware with DAS/RAID on MacPro or Xserve: the Apple RAID controller is not supported with ESXi (any news there?) and for other RAID controllers you have to solve the problem on how to connect the built-in harddisks, that use a proprietary connector! There are kits available on eBay, but I have no experience with them.