I don't think the staff is sold on Miller yet, which is why Gibson/Okoye are in the mix. Gibson will be Miller's primary competition, but I wouldn't be surprised if they try Okoye out at NT.
What was happening last season was the defensive line for the Bucs was always attacking upfield (big no no) leaving huge gaps the LB's had to defend. Whoah whoah whoah. I thought we want to attack with our front 7? Now you're saying the defensive line should not attack?
Actually in passing situations the DL is allowed to pin their ears back.
But Gruden was a big fan of draw plays during third and long situations because of this. Huge gaps are created when the DL immediately attack upfield, so the idea with the draw play on third and long is to try to catch the defense with their pants down (DL shooting up field leaving gaps while the LB's are way back in coverage and the RB is already at the 2nd level). Gruden knew that in a third and long situation an interception was very high so he was playing the percentages.
Basically, Morris' scheme emphasized the DL attacking upfield as if every play was a passing situation.