You would think that rules of formality as laid down by Society would be well-known. Indeed, this is an assumption of social rules- they are generated in the aggregate. Nonetheless, we do have experts who weigh in on these topics, like Miss Manners and Emily Post. Our rules in medicine for interviews and applicants are slightly different than the social sciences, so I wanted to take a brief minute to go over them.
These rules are fairly consistent regardless of the form of communication. You can apply them to any professional academic veterinary interaction- email, phone interview, video interview, or in-person interview. You are unlikely to be corrected by anyone, and opinions on these may differ.
My general approach and advice is to be more conservative. No one is going to look at you strangely if you address the Dean as Dean Smith. But if you call him Chuck, it will be noticed. Maybe not enough to keep you from the short list, but when competition for a position is fierce, why not make yourself the most outstanding candidate you can?
These are in generally increasing order of conservatism:
Do you know this person personally? Have you worked with them extensively, preferably as a peer? If you were an intern and this person was a faculty member, unless you had a close relationship with them, go to the next level. If you know this person and have worked with them as a peer, you may use their first name.
Is this person the Dean? If so, they are addressed as Dean Lastname. An exception may be made if you are interviewing for a Dean position or higher.
Otherwise, use Title Lastname. This even goes for administrative staff. Addressing an email to Ms. Lawrence is a nice, respectful touch. Staff are people, too, and they appreciate being addressed by a stranger in a socially-acknowledged way. Those with doctorates should be addressed as Dr. Lastname.
Can you be more informal than these rules dictate? Sure. But you will never go wrong adhering to these rules in the application/interview phase of an academic position. Once you get the position, the rules may vary depending on your position and institution. But while you are a candidate, err on the side of formality.