no, and no.
first you don't have to be on the latest cutting edge version of the software when you talk about server stuff, and HP clearly stated that will not support older gen hardware from now on and drivers not made for your gen could very likely no work correctly if not supported.. as you said, gen9+ images have drivers for newer hardware and pregen9 has older support, you would you you unsupported drivers on your server?
i asked you this because i've tested 6.7 gen9 images on my microserver gen8 and some vm weren't working correctly giving rw timeout, rolled back to 6.5.. if you major upgrade your hypervisor from 6.5u2 to 6.7 and use drivers that are not compiled for that kernel you are going to have bad time, and newer drivers as HP said will not support older hardware so could easily break your system, same what's going on with new loader images and new kernel in synology.
newer doesnt meen that your performance and stability will be better, expecially if your hardware is unsupported.
and to be clear, b120i it's not an hardware raid controller, it's a fake raid, and no, your statement about driver fails and data lost is wrong since your software raid in the OS of your choice will handle recovery.
ahci means that the physical drivers attached to the sata ports have no HP fake raid layer to deal with, and all of them are shown directly to the OS.. in that OS you can choose if and how handle the raid and what filesystem you want to use.. of example i have my 5 disks setup in a raid5 (actually shr1) array with a brtfs filesystem, but you could use another raid setup (even those that are not supported from your fake raid controller since it's handled by the os - like mdma) or another filesystem like zfs.
that's why most users that have raid controller flashed in IT mode, to handle the array OS side and not in BIOS.. for example some LSI card dont have RAID5/6, if you flash them IT mode you can pass the disks to the os using the controller as a simple HBA card and then handle the raid array in OS, like FreeNAS os DSM.
if you think that using the b120i is protecting you from data lost you are wrong, and btw raid is not a backup solution anyway so it doesnt have to protect you in the first place.