"The Gen10 cards are specifically designed to work with UEFI" - I get that, but the E208i-p also supports legacy BIOS according to its quickspecs. So although HP might not support it, it's not a blanket "absolutely impossible to work".
It's an ML110 G7 - but I have this card in a DL180 G6 at work working fine. Interestingly I've been doing a bit of trial and error with some more E208i-p cards and the ML110 G7.
Having them in PCE-e slot 1 results in a clean install of Windows failing, doesn't even get to GUI bit: WHEA uncorrectable error
Having them in PCI-e slots 2 or 3 can successfully install Windows. If I use the H240's in slot 1, they're fine so the slot is ok
Having 3 of them (E208i-p) in slots 1, 2, and 3 results in the card in slot 2 failing to initialize: controller could not start. Not the card because I swap them all about, it's always slot 2. Slot 2 is fine with H240's.
I need the mixed-mode capabilities (RAID + HBA) of the E208i-p.