It depends largely on where the Celtics rank defensively at the end of the year, the award typically goes to a player on a top ranked defense. Here are the team defense ranking of the guy who has won it the last twelve years.
Garnett (1)
Howard (1)
Howard (3)
Howard (3)
Chandler (5)
Gasol (2)
Noah (2)
Leonard (2)
Leonard (1)
Draymond (2)
Gobert (1)
Gobert (2)
Nobody outside of the top 5 won it, and only one person outside of the top three and I think even if the C's defense is better than most thought it would be a top 3 defense is a tough ask. Also notice nobody shorter than Kawhi Leonard has won it in that time, largely because big man defense gets a lot more attention but also because it is far more valuable than even the super versatile defense Smart provides. In other words it's not likely.
BUT, if the Celtics defense is top 5 then the narrative that the C's defense is soooo much better than everybody thought it would be could drive votes for our best defensive player Marcus Smart.