Lots of people assume that any light colored wood with spalting on guitars is Maple, and it's not too crazy to do so since most of it is - heck, I've done it before myself! We've used lots of woods that aren't specifically mentioned on our "regulars" list. Beech is a different tree from Maple, but as a top wood, and a spalted on at that, I wouldn't think there would be much if any tone difference.
I know what bass you're looking at - it's one of my favorites! I think everything about that build looks just perfect to my taste.