Does the stock headunit on a 2002 Blazer have RCA outputs, or will I need to install my pioneer headunit?

 

no, it does not. but if you are trying to add a sub and amp, look into getting an LOC. (line output converter

 

Plus an aftermarket headunit will always sound better than your stock player. i would suggest the pioneer install versus the line output convertor if you already have the unit.