It has been awhile since I talked to anyone who works at DL, but here is how it used to work
The gate will not close all at once. It goes down in stages and often never needs to go past stage one. If it does go to stage two it may revert back to stage one later in the day.
Stage one is to close ticket sales on site. Anyone with a ticket still gets in.
Stage two is to close the parks to everyone except AP holders and Resort guests. I think if you have a hand stamp from earlier in the day you can still get in, but not sure.
Stage three is to close the parks to all.
So if you have tickets in hand you can get past the gate even if it is in stage one. If it goes to stage two you can always ask about the PS, I have never run into a closed gate myself, so never asked. If not, ask when to check back.
That said, yes I have heard the park gets to capacity on the 4th and this year crowds are higher already.