If you mean do they open the gates a bit EARLIER than posted, it depends.
They generally DO (by maybe 10-15 minutes). But its usually just to let guests in to a further "holding area".
At Epcot, at the main gate, you can go in to just past the "Leave a Legacy" monoliths to directly under Spaceship Earth. There CMs (some on Segway vehicles) will hold until the posted open time, then escort guests (no RUNNING) to both open areas of Future World (did anyone say SOARIN'?).
From Epcot's International Gateway (in World Showcase) guests are let "up the hill" to a rope at the promenade sidewalk level. At open-time, they are released to trot over to Future World (did I mention SOARIN'?)
At MK, you are let into the smallish courtyard BEFORE you walk under the Railroad tracks into Main Street. (This is the area that features the large "Mickey Face" made of flowers.) There is an "opening ceremony" that takes place above you at the train station (usually) and then the guests are let into the MK at the posted open time.
At DAK, guests are allowed to walk through the "Oasis" area, over the entrance bridge to just before you get to the walkway that actually leads to the various "lands" of DAK. There is a very fun opening ceremony with s couple of surprises. Then, at open-time, most guests are headed to (and are led towards) the Safari. After EE opens, I'll bet the main direction of the opening crowds will CHANGE.
At Dis/MGM Studios, guests are let up to the far end of the entrance street (right across from the "call-board").
At open-time, most guests turn RIGHT and head to ToT and/or RnRC.
So, it still pays to ARRIVE early (by at least 20 minutes) before the posted or EMH time. You'll still be in a crowd, but it will be the EARLY crowd.
