I am not totally ignoring your argument, but I would point out there is always Rule Zero. Rules as Written are advisory and help establish a base line for the game. If you go here
http://www.d20srd.org/srd/skills/listen.htm I would say that a reasonable base listen check would be DC 10 (An unarmored person walking at a slow pace (15 ft./round trying not to make any noise - which isn't quite what your your characters are doing) + 5 for Distractions (Roaring crowd + distance from crowd) to locate the general square where your character is located within 5 feet, higher DCs for further distance, but still making miss chances for being blind. If you are actively trying to move silently, that will be the opposed DC for within 5 feet. What is funny is that Krucks is built for entering the Eye of Gruumsh prestige class, which means one of the feats he took was Blind-Fight, not a prerequisite, but one of the feats he chose.
The +20 DC is basically simulating the Blindsense ability. A lot of the listed DC depends on actual awareness of your foes presence, which is not lacking in this scenario.
Anyways, I like Bella's choice of action, blind and deafen the bastard! Especially after poor Gora being split in two... (That Natural 20...sigh, if only I had those as a pc).