Seems overly complicated to me. Also, you can end up getting worse luck than dice (at least in smaller battles); for your 2 inf, 1 bomber example:
Dice: 5/6 * 5/6 * 1/3 chance of 0 hits –- 23.15%
Fudge dice: (1/3 * 1/3) + 2 * (1/3 * 1/3)=1/3 chance of 0 hits — 33.3%
Maybe it gets balanced out by the fact that the opponent also has bad odds, but not to my fancy.
Two defending infantry not having better odds than one other than the extra hitpoint seems…off to me as well.