shavano,
Thanks for reaching out! The ‘tribe_ce_event_submission_login_form’ filter runs just before outputting the login form HTML, and you can see it in action in our docs here on line 1494: http://docs.tri.be/Community-Events/source-class-TribeCommunityEvents.html#1494.
The Community plugin also gets the login form url from ‘wp_login_url(),’ so if you’re using any custom login form plugins that filter on that function, then the Community add-on should honor your custom login form URL.
I hope that answers your questions, but let me know if you need further help. Thanks! 🙂
-Casey-