It's less about the computer and more about the card itself - Talos II and Blackbird both use the BCM5719 chip for their integrated NICs. Basically, you're flashing part of the motherboard with this firmware. A PCIe card built around the same chip might connect the interfaces in a different way, and firmware doesn't generally have a way of poking around to find out how everything's set up from the hardware side of things - it needs to just know this, and that's why there are separate firmware builds for different hardware.

If you flash one of these files to that card, it might just so happen to work perfectly, but it most likely won't. You would need to figure out how it's wired up and modify the firmware with that knowledge. And then you could use the modified open firmware with that specific card model on any computer that supports the proprietary firmware, because IIUC this is meant to be functionally identical.

So in short, no, you cannot currently use this open firmware on any computer other than Talos II and Blackbird, but for slightly different reason than you might think.