IMIRSEL (the organizer of MIREX) hasn't officially responded yet to the conflicts of interest of organizing a non transparent evaluation and at the same time participating in it. What I've heard from others is that they don't see any problems with it.
Btw, has anyone else noticed that they won in every classification category where overfitting is a big issue? However, in a very related category (mood classification) where overfitting isn't an issue (thanks the a human component in the evaluation) they were outperformed by several others.
Furthermore, IMIRSEL never had their name put down on the list of potential candidates. Given the lack of transparency of the respective MIREX tasks I think this is something every participant should have known before submitting their work. Btw, so far it isn't even known who the researchers are who actually did the work. AFAIK, no entry so far in the history of ISMIR evaluations has been submitted without mentioning who the authors are.
Btw, as to now, IMIRSEL are the only ones in the genre classification task who haven't published an abstract (describing what their algorithm does and how it was optimized) yet. (They also haven't submitted one yet for the other tasks they won in.)
Regarding anonymous MIREX submissions I just remembered that at the ISMIR 2004 evaluation hosted by MTG allowed anonymous submissions... and some authors did choose to do so. (However, as I already mentioned in the comments of this post: MTG clearly stated that they did not participate in the tasks they organized to avoid any conflict of interest.)