Is "你们好" (nǐmen hǎo) in actual use for greeting multiple people at once? I just felt like typing "hello" in Chinese in a chat room (with no Chinese speakers in it but what the hey...)

Halfway through it struck me that there's "你们" (nǐhǎo) for hello, "你" (nǐ) meaning you, and what about "你们" (nǐmen) being more or less a plural "you"? In Spanish for "welcome" you can say "bienvenido" to one person or "bienvenidos" to two people, so there could be similar in other languages.

Well my IME suggested "你们好" as first option when I typed "nimenhao", so that made me think it actually is used?

So I come here to ask of ye experts, What actually is the story with "你们好"?
Yes it's in actual use.

But you need use it carefully, because "你们好" is always used when famous people meeting their fans, or teacher meet there students. If you are meeting elders or in honorific expression, you should use "您好" to each person, even if there are many people at the same time.