I've never been to an ECC, but I've been to plenty of EPAs as a non-equity person. I don't know if they run ECCs differently, but for an EPA, they won't even begin giving the leftover slots to non-equity people until they get through all of the people on the equity waitlist ("equity alternates"
, THEN get through the entire EMC list (which is usually a lot, especially for big shows - sometimes well over 100 per day). As a non-equity person, I've been turned away far more often than not. A lot of the time, there are so many equity people auditioning that they won't even see EMCs, let alone non-eq.
Now, since I've never been to an ECC, I don't know if maybe they take people in larger groups and thereby raise your likelihood of being seen. Someone else would have to chime in on that to give you accurate info.