I guess I assumed that they didn't, because "augmentations" weren't referred to as "spells" and I didn't see a reason to omit such a standard detail. If they have spell failure, though, I assume it's only when wearing medium or heavier armor.
Something like that may well be the case. The only other thing I could see as being effected by "Reduce Spell Failure" would be the chance of a Mishap from Use Magic Device. Maybe once you pick up that skill a mishap only occurs on a failure of 15 or more.
