I recently saw an SAT Writing question where a choice was incorrect supposedly just because it used the passive voice. Are answer choices that use the passive voice always wrong even if they're grammatically correct otherwise?
Not necessarily. Basically, grammar is more important than style, and the use of passive voice is a style issue. First, figure out which answers are grammatically correct. If there are two, one active and one passive voice, pick the one that uses active voice. If there's only one that seems grammatically valid, and it uses passive voice, it's probably the correct answer despite its slight issues with style.