Perhaps not.

Egwene knows the difference between women who spark and women who can be taught because she was taught it by AS. AS who maintain some traditions of using the OP that date back to the AS of the AoL even though there's much that's been forgotten. But they do know enough to know the difference between sparkers and learners and enough to at least theorize that they're selectively breeding the population of the Westlands to not channel.

Now compare to the Seanchan:

The Seanchan AS never unified like those of the Westlands. So there were dozens or even hundreds of woman who called themselves AS and ruled as queens over petty little kindgoms. Each of these AS had a handful of students at best, either their daughters or girls they discovered here and there and taught them probably as heirs, enforcers, or something similar. Or these AS saw girls who could channel as potential rivals and tried to eliminiate them. My guess is that somewhere along the line, the fractured Seanchan AS lost the knowledge that women could be taught to channel.

Then came Hawkwing's sons. They naturally had no idea how channeling worked, because even the AS of the Westlands never went out of their way to explain things about the OP to anyone who wasn't an initiate of the WT. So then Deane, in a failed attempt to kiss Luthair's ass, gives him the first damane. This damane was probably a sparker, I would imagine that Deane might not have been aware that women could learn to channel. Luthair probably inherited his father's mistrust and hatred of AS, and the common folk of Seanchan probably feared and hated their AS rulers, so they all were probably more interested in seeing Deane collared than wondering why she could be used on either end of the a'dam.

Now it's possible a sparker who hasn't sparked could test positive for sul'dam but not damane. I think either two things happen here:

1: The sparker eventually channels spontaneously and gets collared. Because she's now an unperson in Seanchan society, her identity is forgotten, and no one talks about her. So the whole matter gets suppressed.

2: Controlling an a'dam somehow allows her to master the OP subconsciously and survive. I think this is the more likely case. We know there are wilders like Nynaeve who use the OP completely unconsiously without ever being aware of channeling. I think this is the case with a sparker who ends up being a sul'dam first. Probably her block involves the a'dam, she can only channel when controlling a damane, and maybe even channels through the damane, so the other damane don't notice that a sul'dam is channeling.