Mario Golf on GBC was like the old NES Golf.
Mario Tennis on GBC, however, was made by Camelot, the same developer for MG of Cube, Mario Tennis on the GBC, 64 and Cube and Mario Golf on the GBA.
So you may be remembering the Tennis gba game that had an rpg lite style.
Actually Mario Golf for GBC was developed by Camelot as well, and was a full-fleged RPG-flavored golf game (and one of my favorite games on any platform EVER!!) IGN scored it a perfect 100%
Here's the Gamerankings link http://www.gamerankings.com/htmlpages2/197858.asp?q=mario%20golf