I've been looking at BM Micro 4K Cams for use with OBS (input only) but those dont output 4k60 via HDMI. They do output 12G SDI though. Do you think I can use 2 of those cams in OBS via a BM 8K Pro simultaneously at 4k60?I can vouch for this working. Use the DeckLink DeskTop Video software (drivers and configuration tool) and OBS will recognize the 8k Pro SDI inputs as a "Blackmagic Device" HOWEVER you have to have something connected to the card inputs. Trying to pre-configure a computer before setting it up with cameras is a losing battle (ask me how I know...)
I presume that the outputs would also work, but haven't tested it.
The one thing to remember (and this is a Blackmagic hardware thing, not an OBS thing) is that if you are intending to use the HDMI capture on the mezzanine card (daughter card that attaches to the main card) you lose the SDI 1 input.