Again, its not like its a registered trademark or anything. But what a trademark does is it says YOU own that name. They don't want other people using the name because they want to market it. K. Rool hasn't been relevant since 2008, why bother marking it as a trademark simply for a VC release? Correct me if I'm wrong, but I don't recall his name being listed with a trademark symbol in past releases.
Now, if his name had been officially registered as a trademark, we would've known already because someone would've found it. Registering a trademark is when you officially file it with the government. It just makes the government more likely to favor you in a court case, but as long as there's reasonable proof the trademark belongs to you, you don't have to officially register the name.
EDIT:
http://www.nintendo.com/games/detail/UmLUMrrxLgdj9i5t0G-AqKZAYvLe8gG3
K. Rool's name isn't listed with a trademark here, though neither is Donkey Kong.
EDIT 2:
http://www.nintendo.com/games/detail/-L-sytPSngSbZEEkyksX6NLu75c8srJS
In DK64, ALL THE KONGS have TM listed after the name, but K. Rool doesn't.