Bathroom vent through existing roof vent
We've got several things going on here:


This is a ridge-mounted, Slant-Back Roof Vent -- it's used to ventilate Attic air to the outside. It should not be used for double-duty for a Bath Fan exhaust. Warm moist Bathroom air will condensate on its underside and can cause moisture damage &amp; mold on the roof sheathing.
As a Slant-Back Vent, the original photo shows it installed backwards. The slanted side is installed to the top to shed rain water; unseen in this photo is the screened bottom side (see attached photo).
As previously mentioned, most building codes require the Bath exhaust to be vented directly to the outdoors. Attic locations should use insulated duct to reduce condensation problems. The exhaust ducts can discharge through the roof, soffit or gable siding -- but a dampered Vent Hood should be installed as well.
If this installation is to be done by an average Homeowner or Handyman, I typically recommend a siding-mounted vent. Retrofit roof vent installations require proper interlacing with roof shingles (not just gobs of tar); a poorly done job will result in a roof leak.