I'm sure there'll be no shortage of unannounced/uninvited attendees.
The problem with this event and the above-mentioned idea is the fact that only a small part of the slaves will be available in the cans. Even if they are hacked, you only get so-and-so many. So signing up for the fight, then letting your gang in on the location to secure them only get you so far.
On the other hand securing all of them demands that you destroy all the opposing ships, many of whom might be your allies or friends. And that for the amusement of a person you might not like IC, too. Silas get's her entertainment, you get your shame and blue-on-blue shit-fest, and your not guaranteed to get the slaves even then.
Unless ofc loads of them secretly work together for one unified goal in mind regarding the slaves and then have all but one warp out and forfeit their part in the fight, granting the victory to a chosen member of this secret alliance. That could be done, but there are no telling how many attenders will be there solo as requested, how many are really working together, or how many alliances will show up on the field.
In the end, the only guarantee is that Silas will be seriously amused and might not even have to hand the slaves over. More blooding victims \o/