Ari- yes, you could do that. The Drerrick as I've extracted it is a world object, so I set the flags to make it show in World editor and CAW. So, put it in your CAW framework and it will show in CAW; put it in your game framework and it will show in World Edit mode in the game. If you want it to appear in buy mode you might have to mod it to set the correct flags.
If you want to add it in-game then you would have to edit it to get it on a lot, so that you can set the fog emitter to the windmill effect. If you want to get it in to your world then you would need to also splice in the Windmill effect from Riverview, just the same way as you got the train into your game.
If you want to play your world with the Windmill in, make sure you have the Derrick file in your game framework files too- or else it will not show up.