I think they may have helped out medically more than the bacteria thing (which I won't get into, since there's a lot of inconsistencies with Chee programming, depending on the ghostwriter... I'm sure I'm not the only one who cringed when Erek electrocuted Rachel.).
But I think if the Chee were to figure out a way to help someone be in better help, they might dip a helping hand in, made a few suggestions.
I'm reminded of a part in The Host (by SMeyer), that said something like "We came to experience, not to change. But health isn't something we can compromise on.", and I think the Chee are much like that. They don't want to dump technology on the human race, since they want to experience their lives properly, but I don't think they'd be comfortable with letting them die, when they could do something to help them. So, they very well could have helped with a few medical advancements.