Thanks for summing it all up, Filux!
Sadly Dave did not report himself so the developers don't have the means to ask him for further details or to work with him towards fixing it. On the other hand, as long as there is no OS X developer with own hardware this won't be possible anyways.
Having read the report, all I can say is that Dave has a well equipped system, which based on its hardware should be able to run MegaGlest very well. This is a dual graphics card system, though, so maybe this could be the source of problems (in the drivers, the X server, or MegaGlest/SDL). His OS X version is the very latest stable release (Mac OS X 10.9.1) so this should not be a problem.
Based on the stack trace (mentioning gleRunVertexSubmitImmediate), a very wild guess is that maybe --disable-vbo may help him.
open -n -a MegaGlest.app --args '--fullscreen=true --disable-vbo'
... with or without --fullscreen=true
He probably won't read it, but maybe some other OS X user can benefit of it.