I really like this signing, and for reasons I have not seen discussed.
A key reason, is how he can help the Colts in 4th and short, and goal line defense. In the those critical defensive moments, I can see a grouping where Grover and Raekwon are both inside, and D-Buck slides out wider . That makes a stout group of men to displace on an interior run. This type of subtle, yet meaningful option, could change a game outcome in the Colts favor.
Another is the change from a 2-Gap anchor & shed, to a 1-Gap push & pursuit. I think he takes to the style and thrives.