Is it good practice to have a film's supporters contact film festival program directors?
Informally, I would think this would be a bad idea - you really don't want to annoy the directors by spamming them with emails.

I speak to a lot of festival directors on behalf of my band (music, not video, but I feel the principle holds true anyway) and what they want to see is evidence of your following, examples of your work, and positive evidence that you will bring in a crowd.

So of high value are:


Social networking - creating 'the buzz' - on Twitter, Facebook etc - not just from you, but form supporters
Targeting high profile supporters or sponsors to provide advertising, merchandise etc
Providing a simple bio and materials for the festival to review and then use


And above all making it easy for them to put on your material and attract a crowd - don't annoy them, just show them why it makes sense.