Problem is and has always been the requirement to look at 100% of the surface being peened for complete coverage. Most specifications require 10x magnification. Some allow for tracer dyes. Unfortunately tracer dyes aren't perfect either. They tend to work best on materials / intensities that are the easiest to inspect at 10x.
Now if you could get your customer to agree to use a sampling plan, where you're inspection predefined locations on the part something like this
https://toyoseiko.co.jp/en/product/coverage-checker-uv/ could be advantageous. If you have to look at the entire part it would be cost prohibitive.