Emissions? It removes the first cat so it may put you out of the limits for smog, etc. I don't live in Cali, but I would imagine it might be illegal unless you add another cat back. Someone in CA wanna chime in?
Depends on what you consider legal. Any headers or modification that removed or changes the location of the cats is considered not street legal in CA. However, it is still possible for the car to pass the sniff test during a smog check. You just have to hope the smog tech is too lazy to look under the car.