Yes, actually. Comiket is the most loose of the events. Cosplay is allowed in a bunch of areas, you don't have to register your camera and video is okay.
As for your DSLR, I've been to some events where they told me not to use the video setting on my camera, haha. But again, if your sly about it, you should be fine. But cosplayers often know the rules and if you ask to take video they could say no.