just cause there is a golf hole already, doesn't make it a good dg hole. if the installed course isn't worth $$$ to play it, they won't be getting any repeat business and will have just sunk $10k to make their problems worse.
i'ld treat it as a completely blank property. utilizing features of the golf course where it makes sense, but also utilizing the woods and other features that may be on course, but not apart of a current bg hole. i'd be willing to bet none of the "best DG holes" on your course will match any of the current BG holes.