When it was decided to go ahead and do a taxonomic system in Opus, a rather arbitrary decision was made to follow Clements 2007. Changes to this may happen when a new version of the major checklists come out, but not as individual scientific papers come out. This is similar to the way common and scientific names are handled in Opus: status quo is maintained unless there is a consensus for a change among the checklists.
And yes, Clements treat all day raptors as falling within falconiformes, including new world vultures. There may be data out there to dispute that placement, but the editors (all of us) of Opus are not taxonomic experts and cannot decide which papers to believe and which not. By waiting until a clear position is taken by the checklist makers, Opus is somewhat more stable than what it would otherwise be.
It would, however, be perfectly acceptable, even great, if you could add a little on the position of these birds to the appropriate Category, probably best to Category:Cathartidae, saying that recent papers suggest another placement, and give a reference if at all possible.
Cheers
Niels