Pistorius had to fight his way into the Olympics. His artificial limbs have been scrutinized, and The Court of Arbitration for Sport ruled that Pistorius has no advantage over other runners during a race.
http://en.wikipedia.org/wiki/Oscar_Pistorius#Dispute_over_prosthetics
He's good to go, and he should be allowed to compete.
The CAS panel unanimously determined that Dr. Brüggemann only tested Pistorius's biomechanics at full-speed when he was running in a straight line (unlike a real 400-metre race), that the report did not consider the disadvantages that Pistorius suffers at the start and acceleration phases of the race, and that overall there was no evidence that he had any net advantage over able-bodied athletes.
http://en.wikipedia.org/wiki/Oscar_Pistorius#Dispute_over_prosthetics
He's good to go, and he should be allowed to compete.