Handful. They also use them in Airborne Brigade, and I vaguely recall one or two others. I wasn't meaning to imply that they are as prevalent as Greatswords, merely that it isn't exclusive to XI. It could entirely grow in the future, depends on what they feel like doing. But the biggest game they've ever used scythes is definitely XI. They seem to mostly use scythes as a way to keep them different from Paladins, but it's kind of silly.

Also, pretty sure that's Cecil from FFIV, not FFIII's Dark Knights.