There was an oxygen harvester called Profac: http://www.bisbos.com/rocketscience/...ac/profac.html
I'm not spooked by the nuclear fuel of this thing, which has to fly rather 'low' to harvest--maybe not as low as this satellite which feels enough drag to warrant fins: http://en.wikipedia.org/wiki/Gravity...ation_Explorer
My fear is a repeat of the disaster caused by the poor mans Centaur:
I seem to remember that a Briz upper stage explosion caused more debris than the Chinese ASAT test and the recent American satellite shoot-down with a Standard missile 3 combined:
And that wasn't even trying to be a depot. Add hypergolics to the mix with a meteoroid, and you can imagine the rest. This is the real reason I favor HLLVs. Dump all you fuel off as thrust as quickly as you can and swap sloshing fuel for inertia that can't leak. Introduce docking and refueling to a zero g environment and you are asking for trouble.