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Volt meters would probably read the same, but the ammeters I think you could setup to read each alternator some how. Not really sure on the good or bad idea part. Now if one alt was for the truck and the second for some aux batteries in the bed or trailer or the like, then it would be nice to watch and see when the amps drop off so you'd know when the aux batteries are charged. I have one aux battery for accessories and such on my truck that I use a volt meter to monitor it. Doesn't really say a whole lot though, just 14 when truck is on and a little over 12V when off for a while.
Unless you are running a very large stereo or heavy electical loads, I'd look more into the coolant temp, actual oil temp/pressure. Or maybe even a fuel gauge for an aux fuel tank(s).