Generally, GoG is great, they have a great user experience, sell most of the best games from my formative years, and represent brilliant value. My one complaint is the odd compatibility hole - I've been waiting for Settlers 2 to become available on the Mac for what seems like forever.
Since it's a DosBox game, why can't you take the GOG installer for Windows, unpack it and run the game in your DosBox on OS X? Some minor .conf modifications which are needed aren't hard to figure out.
