Ah. I know that early on, each manufacturer did it differently. I don't know about now. (Some manufacturers used little cards, others used giant sets of jumpers.) I would say that it depends from motherboard to motherboard, manufacturer to manufacturer.
The only way to find out is to compare the two specific boards in question.
Edit: Looking at your subject, you say you are wondering between an Asus A8N and an Abit A8N.
Abit's closest board to that name is the just plain AN8, which doesn't even have SLI. So I assume you don't mean that. Then the next obvious choice would be the AN8-SLI.
Likewise, Asus doesn't have a just plain A8N, they do have an A8N-SLI Deluxe, though.
Looking at the manuals for the two, their SLI jumpers do look like they have the same pinout. They appear to be based on the standard Nvidia-designed jumper.