The legality of BT as you know is being hugely contested at the moment.
BT itself isn't anymore illegal than FTP or even SMTP and HTTP for that matter, what is illegal is the majority of the content being shared via BT.
Now since you are talking about hosting the trackers, that is a little more involved that just saying "go here and download the illegal content." The tracker itself is a "key" if you will to the illegal content. Sort of like handing a guy a rock to smash a window at Blockbuster to steal movies.
"Hey I just gave him the rock, I didn't smash the window or supply any copyright material (assuming the rock is open source
).
Maybe my analogy sucks, but my point is that to the best of my understanding; yes, hosting BT trackers to copyright content is illegal. I'd recommend to take a peak at the forums over at Zeropaid.com for more info:
http://www.zeropaid.com/bbs/