If the zombies are big enough, the wardancers can rack up +12 combat res against them and watch the vargulf explode. Its not like the zombies are going to be getting many (if any) kills and that diagram showed way more wardancers than you'd need to win that fight, rear bonus or not.
Wardancers need 3's and 3's; with only 3 attacks each with the +1 attack dance. Because they ranked up on Vargie, they are only 4 wide. This means the dancers only come in with 12 attacks. The zombies on the other hand, bring in +7 combat res (if they have a standard); wardancers have no option for a standard.
The odds are slightly in the favor of the combined front charge, with the undead winning by ~3 either way.
That's what really strikes me as odd. This guy didn't gain a numerical advantage, he just came off being a jackass.
-Matt