I guess you folks are aware of the fact that one of the most sensitive issues when cloaking is the final tatget URL. Therefore, placing a pixel on the money page is like merely disclosing everything to fb.
The logic says that if the pixel goes only on the white page, fb will see the gap, namely traffic not triggering the pixel.
The thank you page idea is not, unfortunately, a practical solution because we want the users hitting the target link, not the thank you page, which if it had both pixel and redirect would be vulnerable to same "gap", except the case it would receive traffic only from white page.
The solution would be to load the pixel in some type of temporary header, from where it gets discarded before the real LP gets loaded, e.g., via a redirect. So the temporary header should parse the final URL, redirect and then left behind as the pixel will reside there.