It differs from park to park but just follow the crowd.
MK, AK and EP (I believe) currently allow all guests to enter the park. Non ETPE guests are directed one way and ETPE guests are directed a different way. The is an actual rope and CMs stopping guests from progressing past where they should. When ETPE begins guests will have their band scanned (one person for the group) and be allowed to proceed into the open area of the park.
The division happens before the rope drop area so there should be no need to pass anyone once ETPE begins.
DHS holds non-ETPE eligible guests at a set of tapstiles, before entering the park.