According to the PCI express standards, devices should work in x1 or x4 slots, assuming the x1 slot is cut, or a riser is used. Also, x1 slots support up to 250MB/sec, while dual gbit is 250MB/sec, so why does the EXPI9402PT server card specifically state its not supported in x1 slots? I dont want to buy one and try it just to find out theres a reason it doesn't work.
I know others have used video cards that are x8 or x16 in an x4 or x1, albeit at reduced bandwidth/performance. I can't find much info on Intels site, so hopeing someone here can answer (the reason is I have no more x16 slots on my board, and only x1s.)
The adapter will function in a cut down x1 slot or with a lane reducer, but throughput might be reduced. Do you have more than one x1 slot? You might want to consider using two single-port adapters like the Intel® Gigabit CT Desktop Adapter instead of a dual port adapter.