well, its safest to always use the neutralizer in the kit, HOWEVER, if you run out and you have neutralizing shampoo from another kit or bought on its own (isoplus has one?) its probably not going to hurt to use it to finish the job.
So though I can say yes I've done it and suffered no ill effects, I wouldn't say its ok to do it all the time though (thats me being cautious)
HTH
-A