Nitrite is non-toxic to marine fish short term, even at what we consider 'very high' concentrations. Like 20ppm or whatever. I personally prefer that my nitrite-oxidizers are fully capable of handling all the nitrite produced, but different people have different opinions on this.
Bigger question is, what cycling method are you going with? Dr. Tim's? If so, the question is not whether parameters read 0, but rather if ammonia (and nitrite) reads 0 24 hours after dosing ammonium chloride. Though if you are using the API ammonia test kit, sometimes it just registers as 0.25 rather than 0 and that's fine too.