I think the difficulty in determining who is a part of a Christian film whether all Christian or some Christian cast and crew determines whether someone who makes that film views it as a “ministry” or “vocation”
See if someone starts a church and then brings in the staff - Pastor, preachers, choir, music minister, deacons, etc… well then everyone in those positions are most likely Christian. If that church puts on a Passion Play or a play based on the Birth of Christ, most likely everyone in that play is going to be a member of that church and at least considered to be a Christian..
So on a Christian film, if they view it as a ministry or part of a church rather than vocation - they might look at it the same way.
And even someone like Rich Christiano who views Christian filmmaking as something more like ministry or preaching to the choir, he is still open as far as I recall from reading and listening to him speak to having non Christians act in his film.
