I seem to remember Ryan clarifying some pronunciations in a thread a while back, but there's no guide. Any particular names you're having trouble with?
Most of the time it doesn't matter, as long as you're consistent.
When I was trying to sound out Ragesia for the first time, I was stumbling over the words. My friend said something similar, "Dude, who cares, we won't know any difference."
@Jhaelen Apparently the German influence in Wisconsin extends beyond beer, brats and polka into word pronunciation as well . Pronouncing "Ragesia" any other way seems ... off.