Okay, answer from 'Mikachu' in #openbox:
The shortcut for the super key is either Meta_L or Super_L (Or _R for the other key).
However, this will override any other combination that uses that key!
I actually may make this change, and come up with different shortcuts for the apps I need, but I'm reluctant to change any OS defaults too much. Every change is something I have to remember to backup/reconfigure if/when I reinstall. 
--
The scrollwheel/desktop switcher may only be a problem for me, because have the a.d.d. tendency to click and scroll my mouse on random crap when I'm thinking. If you want to turn it off, find the relevant bit of code and comment it out, thusly:
<!-- Scrollwheel switches desktop and pisses me off
<mousebind button="Up" action="Click">
<action name="DesktopPrevious"/>
</mousebind>
<mousebind button="Down" action="Click">
<action name="DesktopNext"/>
</mousebind> -->
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