As AOL and Yahoo continue their transition into one platform, things were bound to change over time. As a result of this ongoing consolidation, AOL no longer offers whitelisting of sending IP addresses. Though the form still seems to be up at the moment, any submissions seem to get a reply from the AOL Postmaster robot saying, "Whitelisting is no longer offered or needed for mailing to AOL. If you see delivery issues please sign up for a Feed Back Loop at: https://postmaster.aol.com/fbl-request"
As the net effect here is that AOL seems to be moving onto Yahoo's platform -- if you're wondering how to troubleshoot AOL delivery issues today, the general deliverability guidance for Yahoo is probably your best place to start.
For now, it seems as though the AOL Feedback Loop is still in effect. I do suggest registering for it as long as it is still possible, but also, be sure to sign all mail with DKIM and register with the Yahoo FBL as well, so AOL users are covered on both sides of the possible feedback loop equation.