Does the lack of lights mean the ethernet ports are dead?
If you have ruled out the other possibilities, cable, switch, then yes.
Is there anyway of resetting them?
Not that I'm aware of. When your disks still spin up I guess the power supply is still alive. In this case I'd expect some power regulator to be faulty. It might be an idea to look if you see some obvious defect capacitors on the motherboard, near the ethernet port.
Can I take the motherboard out of our other none working 5 big (heat issue) and put it into the one with the bad network ports
What do you mean by heat issue? Broken fan? In that case you'll have to transplant the fan either.
And about the possibility, I don't know. Some XBig systems have an eeprom, containing the UUID of all internal raid arrays, and it will just refuse to boot if it doesn't fit. Don't know if your box also has that. But AFAIK it won't harm your data, in that case, it will just refuse to mount the array.