MacOSXRumors reports that the next major revision of iChat AV will will have AOL/AIM video-conferencing compatibility... while interoperability with other protocols is not expected, according to the rumor site.
AOL's AIM with video conferencing is currently in Beta testing... and several readers have reported that AIM Beta users appear in iChat with a greyed-out Video icon next to their screen-names. As a result, the two applications do not presently allow inter-app video conferencing.... but do recognize the existence of the video-capabilities of the other application.