Yes, the firmware is different, and that is why OMSA can't detect it. 

You can try to force-flash it with the server version so it will work with the server, but you would likely need a linux version:

http://www.dell.com/support/home/us/en/19/drivers/driversdetails?driverId=R09PJ&fileId=3586834610&osCode=BIOSA&productCode=poweredge-t420&languageCode=en&categoryId=SF

This is the kind of thing that happens when you go off-plan and do your own thing with unsupported configs :)

Thanks - that got me one step closer. I was able to get the latest Poweredge firmware to install and it seems happy, however, it's still not showing up in OMSA. I have a suspicion that it's because it seems that the PE firmware didn't do anything about the '1f78' SUBDEV that identifies it as 'H310 for Precision' when you load the Windows drivers. I tried flashing the sbr image that was included with a zip that had a bunch of firmware meant for converting over tot he LSI firmware that was supposed to be a stock H310 sbr, but either the 'SUBDEV' is not part of the sbr, or that stock sbr file was from another 'H310 for Precision'.

Does anyone have any ideas how to change the SUBDEV on the card so it's recognized as a Poweredge H310? Given that best I can tell, the hardware is all the same, it seems rather dumb that there is different firmware and IDs for Poweredge vs precision. Why not have 'H310 firmware' and who cares what it's in?

For system compatibility - the systems they go in are radically different. One size does not fit all.

Did you get any farther on this issue? I want to do the same thing! I feel kinda left out since Dell abandoned updating this firmware and kept updating the server versions....

Also, what do you think of flashing the card with IT firmware? I have seen a couple blog posts on it. I can't afford to experiment on it though as it is in my workstation at work!