Can Evangelist select a Prestige Class as its aligned class?
Evangelists come from many different backgrounds, and they show an unusual range of diversity. At 2nd level, the evangelist must choose a class she belonged to before adding the prestige class to be her aligned class. She gains all the class features for this class, essentially adding every evangelist level beyond 1st to her aligned class to determine what class features she gains. She still retains the Hit Dice, base attack bonus, saving throw bonuses, and skill ranks of the prestige class, but gains all other class features of her aligned class as well as those of the evangelist prestige class.
Technically yes… but you will find that most GMs don’t allow it. It’s largely understood that by RAW it works but by RAI it shouldn’t. In almost every conceivable situation allowing Evangelist to select another prC as its Aligned Class is very much overpowered and potentially gamebreaking. It is already insanely potent when applied to just a regular class.
I'm in agreement that you can, but that you probably shouldn't. Since prestige classes being available are always under the purview of the GM anyway, it is their call regardless.
Now, if they do permit it (and in some cases they do), it gets real silly when you chain Mortal Usher or Esoteric Knight into the mix with Evangelist. I've theory crafted a character or two doing this, and it can turn the less ideal combinations into something decently powerful.