Basically, this is a CYA for the con. If any companies come and complain that the con was showing their licensed footage without their permission, the con can point to the release and say that the company needs to talk to you. To be fully, un-sue-ably legal about it, yes, you would need written permission. Is anyone going to do it? I'd be fairly surprised if anyone did- and even if anyone tried, the odds are that the music company would not give their OK (and there's a good chance that the anime companies wouldn't give written OK either- they have copyrights to protect).
Bob 'Ash' Babcock
Electric Leech Productions