Is the temp of the water in my swamp cooler a good indication of the temp of the fermenting beer?
Yes and no. If your fermentor is fully submerged in a tub of water the water in the tub will be near the temp of your wort at the center of the fermentor. If your fermentor is partially submerged you will need to cool the outside of the fermentor to a greater degree to moderate the temp at the center of your wort.
After about 12 hours