Corrected entry: Peter absorbs René "The Haitian"'s abilities (erase memory and neutralize abilities). Later on he fights Sylar and uses René's ability to force Sylar out. Sylar faints and turns into Nathan. If Peter absorbed René's abilities to neutralize abilities, shouldn't Sylar be unable to shape-shift into Nathan's looks?
Corrected entry: Peter absorbs René "The Haitian"'s abilities (erase memory and neutralize abilities). But, shouldn't Peter's ability (to absorb abilities) be neutralized around René, therefore making him unable to absorb his abilities?
Correction: The Haitian's powers are not always active. It's a manual power, meaning that the user has to consciously use it.
Correction: As shown in season 1 when Nathan is able to fly away from the Haitian and Bennet, abilities can be used when near the Haitian if he is not intentionally turning off other peoples abilities, so to speak. In this instance, Sylar has passed out. Peter sees no need to nullify his powers at that point, so the shape shifting is able to transpire.