AFAIK helium is only used to prepare the fuel and oxidizer lines for burns and to backfill propellant tanks. Liquid propellant has to be kept extremely far below zero and if the lines aren't 1, down to apropriate temperatures and 2, clear of anything that isnt rocket fuel it can cause some serious damage so helium is a purging gas. Also as the propellant is used they have to keep the fuel tanks pressurized with helium to maintain a higher pressure upstream of the engine. You dont want an engine to burn backwards.

That being said, this mission wasnt slated to take extremely long or be particularly complex (im aware oribital mechanics are by default complex but its just a mission to and from the ISS, no midflight reconfigurations like the saturn missions).

Mission control is full of engineers who know this rocket better than anyone else ever will. If they had reason to believe a small complication isnt worth worrying about we have no choice but to believe them. There are so many systems in place for a rocket launch, there has to be some wiggle room in terms of non critical systems and issues. Its kind of a morbid fact that if we dont launch until it's 100% perfect nothing would leave florida.