Everything in the onion family is healthy due to antioxidants, mineral content, and anti-inflammatory properties. They help lower triglycerides and prevent blood clots. They are also effective for indirect birth control and crowd control.
Sure. I've seen a few places that have young red onions that are used like green onions. I guess some are called spring onions.
In Asian cooking, green onions are ubiquitous. The Chinese language is set around that. The word for green onion/scallion is 葱 (cōng) while the words for onion are 洋葱 (yángcōng), which literally means "foreign scallion".