Since I couldn't get back to sleep this morning, I decided to do a bout of wild speculation instead.
There's ongoing work to check the DNA of Ganger-Rolf's heirs in Rouen to ascertain their ancestry. I started wondering about the other side of the question: Do we have someone to compare them against?
The result is an analysis of whether we have male-line descendants of Ragnvald Mørejarl in the Geni database that could be tested. It turns out that there are - but they're all descended from a single ancestor around 1500, and this ancestor does not have documentation on Geni.
Analysis here: https://wiki.geni.com/index.php/Descent_from_Ragnvald_M%C3%B8rejarl
Take it as entertainment! (unless you have a friend in this family group that could be convinced to test!)