I'm pretty sure you're reading too much into these "stealth ninja" submissions where a song shows up in playtesting out of the blue --- it's not that the band/author didn't *want* to make a special announcement beforehand, it's more likely that they didn't even know they could. (Pretty sure that not many of the bands/labels in playtesting even know or care that this forum exists.)
And I'm also pretty sure that if you polled the playtest ninjas about the subject, the majority would be perfectly fine with more exposure on this forum and anywhere else they can get the word out. I've read a lot of the Myspace pages of the bands who are submitting material, and a large number are absolutely bragging and blogging about coming to RBN; they'd have no problem with these thread announcements whatsoever.
As for "rights," though --- yes, we all have the "right" to post this information, since HMX has already said so. It's public information, and readily available (again, a $100 subscription to the Creators' Club does *not* require an oath of secrecy).