I've seen elsewhere that scrolling via the mouse wheel (and other mousy events) can be enabled for tmux.. can this feature also be enabled in byobu (over tmux) and how?
Yes, this is possible. You just have to enter scrollback mode first.
Simply press F7, and then use your mouse scroll wheel. Finally, press ESC to exit scrollback mode.
It appears that some terminals won't allow you to scroll using your mouse still. For Gnome Terminal, untick the Scroll on keystroke option in the profile preferences (tab Scrolling).