This subject has been cussed and discussed many times before, but the posts above this one give you the gist of the situation. Yes, the bikes with O2 sensors can adjust for minor changes in air flow through the engine, intake or exhaust. So while the bike may not run any leaner than stock, assuming the changes are within the range of adjustment built in to the system, it won't run any better either.
I guess if the entire exercise is just aimed at making more noise with an exhaust change, and you don't care if the bike runs better, then you will be good to go. Of course, you will forfeit the improved performance, driveability, and reduced operating temps that would result from tuning. And that last item, temps, isn't just about making the rider more comfortable.
Jerry