I think people's replies to this thread are commonly confusing ascending without modifying source with ascending without reading source (even though some people have answered correctly). Just to clarify the two different issues, there is only one person known to have ascended unspoiled.
However, people frequently ascend without modifying or tampering with the code. Essentially all of these people have been spoiled by studying source code or spoiler files derived from it (although some people study spoilers extensively and some people just consult them for very specific topics). You can see ascensions in real time every single day by watching other people play on nethack.alt.org. Especially on weekends, there will be several victories per day!
https://groups.google.com/forum/#!topic/rec.games.roguelike....
However, people frequently ascend without modifying or tampering with the code. Essentially all of these people have been spoiled by studying source code or spoiler files derived from it (although some people study spoilers extensively and some people just consult them for very specific topics). You can see ascensions in real time every single day by watching other people play on nethack.alt.org. Especially on weekends, there will be several victories per day!