is this form from aadsas optional or required? also, it says that updates will be sent only to those schools which participate in the academic update... anyone know which schools those are?
It's optional. In theory it is only for those applicants who haven't heard from schools yet and want to update schools with their fall grades that may have not been on their application at the time they submitted.
If you are already in, or don't think an update will convince schools to interview/accept you, then I wouldn't worry about it.
AND, it's probably easier just to send transcripts to schools if you do feel that you would benefit from sending them newer grades.