Is it okay to play fingerstyle on an acoustic guitar with the index finger on the high e string and the ring finger on the g string instead of the ring finger on the high e string and the index finger on the g string?

Personally I would find that uncomfortable. The key to playing guitar though is to find a technique that is comfortable for you, but it must also be comfortable and not damaging over long periods of time. If your technique puts strain on your hands/wrist/arms you can end up injuring yourself quite easily. 
The way to test whether or not it is a good technique is to pick a phrase that you can play and play it to a metronome for a couple of minutes. If you start feeling strain anywhere you should stop and change your technique.