I thought I would take a gamble on this.
The onboard controller does support pass-through ahci.
However, it doesn't come with a mini sas cable. The controller based mini sas cable for the 9211/M1015 (sff-8087 to sata) is the wrong cable for this board. The mini sas cable and back plane from an n54l (looks like a Mini SAS SFF-8087 Male to SAS SFF-8482) will work, but that's a bad idea. Additionally, the mini sas in HP 730641-B21 kit is a single drive cable.
Going on, it's expensive ram, expensive expansion, poor cooling, and moving it to a custom case is an utter pain.
For me, it's been a $400 mistake (ram, fan adapters, expansion kits, and the $250 server) and I'm not even done yet.
Do not buy an ML10 for the purpose of freenas storage. An n54l is a better move for support and far less pain. Take a look at some of the other builds on here instead.
On the other hand, if you are looking for a cheap 2008R2 server that will only need 2 sata devices, the ML10 makes sense.