bytesized hosting has the following rule:
We do not allow the use of torrents that are registered on a tracker that allows anyone to sign up without an invite. The rule of thumb is: If you can get a .torrent file of the server without an invitation, then the tracker is banned. This policy is enforced through our firewall as well as scanning for torrent files containing trackers that are publicly accessible. [...]
This might be a problem for bitcointorrentz, as probably people who already have access to a private tracker will also need their torrents to be seeded properly, have less fear to be prosecuted and less need to pay for such a service anonymously.
If DHT works + is allowed though, I guess they could be fine, as through Peer exchange you'd get enough peers/seeds anyways quickly then.