I have two Dahua 5231ze cams and I have a need to properly mount them on the soffit of my home.... So, can I simply screw these to the soffit or do I need the junction box (PFA130-E)?
Vinyl probably won't hold it. Many of us have used aluminum stock to attach them to and then wiggle it up in the span.
You can shove the wiring back into the soffit, just make sure to properly waterproof it. Dielectric grease and that tape that seals itself. But you should do that even if you use the junction box.