I'm guessing no (unless you would need to use a different command for using Safari's default webkit, but I couldn't find anything). I tried it in default Safari and it didn't work, but I downloaded todays nightly and it works fine. (It's really pretty neat.)
If you wanted similar functionality in the default Safari (w/o nightly webkit) you could always just enable the debug menu and use the 'DOM tree' I'd figure (though it's not nearly as nice as that new Web Inspector).