Yes, new underlayment would be called for to do a good job with this product or really any glue down product. You want the floor flat (the flatness standards are listed in the installation instructions) but are generally within 3/16" in a 10' span in any direction. And you want the floor smooth. No staples sticking up, no edges on the underlayment being higher or lower to the adjacent panel, to "proud corners" on the underlayment. Seams should generally be smooth and filled if any gaps.