Resurrecting a dead torrent tracker and finding 3M peers

> Is this legal?

Why wouldn't it be? You're not actually hosting a tracker in this case, only looking at incoming connections. And even if you do run a tracker, hard to make the case that the tracker itself is illega. Hosting something like opentrackr is like hosting a search engine, how they respond to legal takedown requests is where the crux is at, and whatever infra sits around the tracker, so police and courts can see/assume the intent. But trackers are pretty stupid coordination server software, would be crazy if they became illegal.

Do you think the police understand this nuance? Especially since most of the traffic that will go through there is probably copyright infringement?

They'll just see tracker and assume it's illegal.

Tell them it's for training a corporate AI model, then.