I have mashed with roasted, seeded, and vained jalapeños, and added some additional flesh at flameout. The beer was a dry imperial pale ale and I used about four large peppers. Together, the additions gave the beer a very nice, gentle jalapeño aroma and imparted a similar flavor. The late addition hops were of a less noisy variety and the quantities restrained to let the peppers shine.
Well, since I like heat, I decided to see if I could make the beer hotter and tossed two seeded an vained habanero peppers into the keg for two days. The alcohol sucked the capsaicin straight out of them and I was left with fire beer that had a wonderful habanero aroma and an amplified flavor. The hops were still noticeable but were wrapped in a blanket of spice. The jalapeño contributions were essentially erased.
So hopefully this gives you an idea of the possible results to expect from different pepper additions, especially in an American pale type of ale. With roastier beers, you may want to up the aroma additions or consider just going for a light burn by adding some fruit directly into the fermenter.