I don't know well about "out there". Isn't it okay to use only "they're somewhere" without "out there"?
"Out there" here means "somewhere beyond my immediate surroundings". Just "somewhere" implies someone or something can be anywhere, including near you. Therefore, while saying "they're somewhere" is not wrong, saying "they're out there somewhere" is more specific and better to say. Ex: Dangerous animals are out there. (Meaning dangerous animals are not near you, but somewhere away from your location)