This may not be exactly in the Green Bay/Appleton area, but it's about the closest you'll find (ok...some possible legends/sites around Oshkosh and Fond du Lac, too, but they're very sketchy). Crivitz supposedly has one called (pardon the slur, but this is what it's called) Nigger's Hill. The stash was payment for furtrading to "Redbeard" (fur trader, not a pirate) and two associates, one of which was a very large black man...hence the name of the hill. The group was murdered by Indians being used as pawns by another group of traders in and around Green Bay. Do a search "Crivitz buried treasure" on the Wisconsin Historical Society website. There is a fairly lengthy article from the Wausaukee Independent in March 1917. Still no clue if it has ever been found.
Now that that's out of the way, "hi" everybody. If it's of interest, I plan on doing a MD around Gotham and Arena, WI along the Wisconsin River either later this fall or next spring. There are a few sites I've been researching and want to take a weekend to do some field work. I don't expect to find anything off the bat, but knowing where they're NOT buried helps just the same.