I recently found a partial attempt to fix arc's gensyms on Anarki. I say partial because although 'uniq now returns uninterned symbols, 'ac-global-name still automatically interns them (in order to add "__" to the front) when they are evaluated. Thus name capture is still possible:
I believe the appropriate fix is to keep 'ac-global-name from automatically interning gensyms. I posted one possible (though ugly) solution at http://arclanguage.org/item?id=5104, but didn't commit the change because people didn't seem terribly enthusiastic at the time. Considering that someone else seems to be concerned with Arc's gensyms, I may commit a fix if I have time.
