I'm not sure I understand what you mean when you say Marius granted citizenship to his Italian auxiliaries. Plutarch says he granted citizenship to 1000 men of Camerinum, and that caused some controversy, but that isn't very many and not particularly a departure from Roman tradition.

The "Marian Reforms" are another thing - we're not sure what those reforms exactly were or how Marius was involved. It's sort of an academic shorthand for changes in the Roman army that took place over time, but that are hard to pin down. I don't think many people think Marius actually reworked the whole army in a decade.

Rome did continue to use Italian auxiliaries. Rome never stopped using auxiliaries as a matter of fact; the population of auxiliaries was just drawn from different ethnic groups, so that in the Late Empire you have all these Germans fighting in Roman armies.

Who rebelled in the Social War seems to have been governed by community relationships to Rome. Basically all the communities that defected to Hannibal revolted again in the Social War. No Latin communities did, and we don't hear about any new Roman citizens like these 1000 men of Camerinum joining the Italian rebels. That might be the result of our poor sources for the Social War - our first narrative source is the 2nd century CE Appian, and he seems to have trouble understanding the relationships of Italians to Romans when they change citizenship.

Maybe if you elaborate more I can provide a clearer answer?