After going through my internal connections, I was led to the email
address of who would be my future coworker. We both would manage a
team of developers.
Is it ethical/appropriate to send them an email to connect with the
intent of potentially applying for the position? If I could get more
information from someone who is in the position I am ...
Training classes for this skill often call it "active listening."
You are right, it's a valuable skill and rare talent. Cultivate it in yourself. (Maybe find one of those training classes?)
And be careful to avoid "triangulation," which is a ten dollar word for "getting caught in the middle."