I have a 2003 Tracker, so its not exactly the same, but I have read on this forum that you may run into problems. Your wheel and tire size will match up fine (I am infact running 235-75-15's on 15" x 5.5" wide factory steel wheels). There will be some body/frame rubbing, but you can cross that bridge when you come to it. The spacers will solve most of those issues.
The problem I have heard is that the Grand Vitara has bigger brakes (calipers) which will not allow the 15" wheels to be installed. If you have them lying around, just pull the wheel off your truck, and try to bolt on one of those 15" wheels. If it fits, you may be in luck.
Like I said, by Tracker is a more stripped down version of the Grand Vitara (no V6, and I believe smaller brakes). This is why the 15" wheels fit some and not other GV's and Trackers. Give it a try, and let me / the form know.