Sorry it took me so long to respond but, unfortunately, the answer is no. I work in rez and can tell you that the load on a flight and the unassigned seats are not related to one another. Some people don't choose their seat ahead of time because they can't sit in their "preferred" seat or maybe they have a large group and want to wait until airport check in to try to sit together. Other times you can see the seat map online and note a lot of open seats but they may be blocked for tier level fliers or the airport is working on something for the plane and are blocking all seat assignments temporarily.

I guess what I'm trying to say is that the "open" seats online is not a good way to choose a nonrev flight. The best way now (and will probably always be) is to call the nonrev line for those airlines who have one (Alaska's is 1-877-677-2566) or the regular number for those who don't, politely introduce yourself as a nonrev and ask about standby. At AS we are happy to give percentages but aren't supposed to give actual counts. I know everyone around me tries to be as helpful as possible because next time the person on the line could me one of us!