The benefits from analytically shifting your point of view, or from using different approaches in different situations certainly don't necessitate actually hallucinating people talking to you. (Hint: Only the latter finds its way to being a symptom for various psych disorders.)

"You need to hallucinate voices / people to get the benefit of viewing a situation from different angles" is not an accurate inference from my argument, nor a fair description of IFS, which as far as I know doesn't include sensory hallucinations.