Absolutely you can use two. The problem lies in fitting them into the engine compartment. The only time I've ever done it was on a full-size Suburban, we fabricated a bracket to hold two. It also took us about 4 hours to get the right belt in place, since GM didn't make a "1996 Suburban 5.7 liter dual-alternator belt".
You'll probably want to keep them isolated from each other electrically as well, although I'm not sure what it would do if you didn't. Like for example, if you were using a lot of audio amplifiers, then leave the stock alt. on the stock battery, and put the second one to a different battery (or batteries) to power the audio system independently.