When you install an application and it asks for your password to continue, entering that password allows it to operate as root to normally modify system files or something similar.

Having root wont do you any good to get the wallet file in itself, but the moment you log in as that user and mount the encrypted drive, it will be accessible by root as if there were no encryption.

I'd say it's a rock solid setup, and until Macs become a much bigger target it will continue to be.  Just be mindful of what applications you allow to install on your system.  There was a recent Mac "virus" that was just a file distributed to people.  Only the people that decided to install it were infected.  Stuff like that is what you'd have to worry about.