I don't know about L-ornithine Aspartate, but Arginine Aspartate is proven on GH output, antifatigue and immunity.
Sanofi Aventis sell it under name: Targifor (in Brazil) 1.5g of L-Arg-Asp for imune support and stamina, and I can tell it works, I get rid of any cold with 3g a day!
If Ornithine Aspartate works similar it would be a great addtion both pre and post workout, but I agree with mr.cooper, it's probably better spent pre workout.