Yes and no.
From my limited knowledge on the subject, the chip you are talking about will be a piggy back ECU. This will take what you tell it at the throttle and modify it to tell the ECU to give more fuel/air than it normally would at that throttle/rpm. However, the 350z has a learning ECU. So it will say "woooah there, you cant have that much sh*t, I'm going to cut back on it cos I know better then you". So the piggy back ECU can tell it all it likes to give a certain air/fuel, but the ECU will eventually tell it to feck off. The only way to get around this is something like a Utec (sp?) which truely controls the system rather than its inputs, but costs big bucks - around the £1500 region to buy and map properly - and gives very little bang for buck.