The NIMBYs in the area are the three neighbouring cellar doors,...

The NIMBYs in the area are the three neighbouring cellar doors, including the one named after the historic mine workings.
I have previously heard at least one longtanding farmer who supported it.

It's hard to use truck traffic as an excuse not to support development. Behind the cellar door, a winery is a factory that takes raw materials (grapes) in and ships products out. A vineyard is a farm with fertiliser, harvesting equipment etc. I can't remember if those sites all have their own bottling lines (empty bottles in, full ones out) or export wine in tankers and return some in cases for retail sale.

People still by French Champagne, despite it having a nuclear powerstation in the area. Hunter Valley has coal mines (one of the major vineyard owners is BHP in the mine buffer zones). A small underground gold mine is not going to destroy the image of the Adelaide Hills Wine Region, which has had many gold mines in history.