Haha! Comeon now you're going too far!
Bamboo pulleys! What's next, bamboo leadscrews? Bamboo linear rails?

Ahh just kidding. If you soak enough varnish into that bamboo pulley it will probably be as good wearing on the splines as most plastic ones. I'm not sure how the interface to the shaft will hold up as that's where all the torque forces will be highest.