I have and E520 working the internal Sata drives, and have been able to boot various version of OSX up to an including Mountain Lion. I use myHack to help with the basic installation, BIOS set to Raid On, and added a modified AHCIPortInjector.kext (attached) into /extra/extensions.. that's it to fix the SATA drives.
AHCIPortInjector.kext.zip