Is unity gain a real HT bypass?

I'm looking at maybe purchasing an older preamp that has a unity gain setting that is meant for connecting an external processor. Does anyone know if this is a true ht bypass that avoids the preamp's processing circuitry, or will running the ht signal through this path noticeably affect the sound? The unit in question is a bat vk5i, though I'm also curious about this question in general. Thanks. -Dave