Will the vented grid lock and/or coin grid lock tiles follow the contour or low spots on the garage floor where water normally will puddle or do I have to fix those low spots first? Is shimming an option? How?

The Vented Grid-Loc and Coin Grid-Loc tiles are a hard plastic tile. They will not contour with the low spots in your floor but will lay over top of them if they are small. If there are large low spots, you may have issues with the tiles interlocking properly. In this case you would have to fix the subfloor for the tiles to properly interlock. Shims probably would not work in this situation because they are typically used to fill small gaps or spaces between objects.