Although it is a vent, Moisture from the shower will cause condensation under your ridge vent. Sometimes a bath vent can transfer enough moissture to do as much damage as a leaking roof. A roof Jack isn't that major to install. Take a hammer up on the roof and tap back and forth, you will feel and hear the rafters under the decking. Cut a 4-5" hole between the rafters and trim the shingles back a little at a time until the roof jack fits over the hole.
Do it right and you won't ever think about it again. Mess it up and it'll be a headache waiting for a rainy day