Does Roof Underlayment and Bitumen are consider a Secondary Water Resistant?
Yes. The roof-covering material is the primary barrier, the underlayment is the secondary barrier.
If you are speaking of a wind mitigation report in Fl, the answer is no. The secondary water barrier muxt be a self adhering polymer modified bitumen roofing underlayment applied directly to the sheathing or a foam
adhesive SWR barrier (not foamed on insulation) applied on every sheathing seam. It goes directly on the sheathing prior to the felt, or other underlayment.
What do you mean by Bitumen.
The underlayment is a yes but are you asking is a caulk or plastic cement a water proofing layer?
Please explain the use of Bitumen.