EDIT: Testing 3.8-9 now, will report back shortly w/ results.
NOT working in release 3.8-9 either…BOOO 
EDIT, my profuse apologies, forgot my own dang post and how I resolved this before when i hit this wall, critical to have HBA attached from the get-go/initial install otherwise mpt2sas throws a fit. Dunno why 3.8-7 plays nice w/out adding from initial install now for me but 3.8-9/3.8-10 does not work w/ VTd unless configed prior to first boot/install.
Rockstor 3.8-8 on vSphere 6.0 U1 storage issue (right near top)
Uggh, damn my lame memory. LOL