According to a few posts on twitter I have seen, yes. They are still checking. Apparently it gets "more lax" after the game starts and people have been sneaking in. (Kind of sad it comes to that) I've seen a few pictures this year of the bottleneck AFTER getting through the gates having to have your ticket scanned a 2nd time to get on the concourse.
Stubhub has it setup differently for different venues/sports/etc. However with Sox games you can buy tickets even after the game has started. Last week some upper deck tickets were going for $1 after game start. I'm not sure the exact time limit after game time you can buy, I feel like its 30 mins. I'll keep an eye on it today during the game.