The "Rules" disallow wearing kit from a team you are not a member of.
However, I believe there is an exception for teams that are now defunct. Leopard Trek is defunct, therefore you're good.

I picked up a Leopard Trek jersey a while back. Have yet to wear it (too cold) but cannot wait.

That said, one of the guys that we ride with shows up in full RadioShack kit (2010) occasionally. No one would say a damn thing to him. Might be because he's state champion for MTB, Cat 1 or 2 CX, and could pound most of us to death on a recovery day.