That isn't a creator I would have thought of, since it seems like fans "in the know" totally respect him, but I guess you're right. In a way, Sakai reminds me a bit of Don Rosa. Uber talented and influential, but because of the books they work on they get passed over by a large contingent of comic fans. I do know that Rosa is big in Europe. Is the same true for Sakai, over seas?
Usagi Yojimbo has been translated into 8-10 other languages, so he has an audience overseas. Not really the same as Rosa, because Rosa has the Disney component which is insanely popular in various parts of NE Europe, and he really stands out from the average creators on the Disney stuff.
Rosa & Barks have similar problems with recognition in the USA because of their complete lack of Marvel/DC work to get them noticed by the vast majority of fans.