Well, considering I thwapped someone else for just such a sort of thing ...
IMO, the main 'mystery guest', the one giving the orders there, was Dunkelzahn himself. The Big D was not the sort of individual to gather together such a notable crowd for the purposes of commentary just for them to comment among themselves; in previous fiction (when he went to talk to Harlequin, with Frosty there) it was made clear that he wanted to tell the world quite a bit more than they already had, but the Laughing Man talked him out of it. Doing so 'anonymously', with himself as a supposedly equal victim, is just the right amount of twistiness.
The other guest (IIRC, there's only two) is an otaku -- speaking about 'channels' and all, that's pretty obvious. Specifically which otaku does not, I think, matter, but considering how many info-pies Dunkelzahn had his talons in, it would not surprise me if he had enough connections with one, or many, otaku who would be willing to do just such a thing for him. Probably without pay, just on a lark ...