Let's look at what the regulations required:
§339.9(c) required the notice to be delivered to the borrower(s) within a “reasonable time†before the completion of the loan.
You can do that by various means. I don't believe the Flood rules discuss e-sign compliance. You must simply be able to demonstrate delivery.
The bank shall retain a record of receipt of the notice by the borrower and servicer for the period of time the bank owns the loan. \ [§339.9(d)]
This can be satisfied by them signing the notice at closing. There is no timing to this requirement.
As you said, "if you comply with esign" you can demonstrate delivery [339.9(c)]. If you get confirmation of receipt and retain it, I believe you satisfy 339.9(d).