Update:
I've tried a load of different versions of the hpsa driver, none of them seem to work correctly as described.
Weirdly, they do detect the logical volumes, but writing/reading to the disks is impossible.
I've attempted to use different flags as described in the KCLASS3B section, but as you say it's very kernel specific and changing these flags causes the driver to not compile for various reasons.
It could be useful to get the source code to the 5.2 XPEnoboot loader, so the working driver in that binary can be inspected, but I dont think this is an option.
I am also not too sure if I can enable SSH during the kernel boot/install time, do i have to plug a serial connection into the box to view the Kernel output / view logs?