Morris was #4 in ST teams tackles, even with his injuries.
I don't know how many of the ST unit he played on, likely 4-6.
We could do a lot worse with our #5 RB spot. Morris won't be expected to take anything but emergency reps, but he can if he has to. He'll probably be on the short yardage team also, until Ridley is ready.
I don't see the downside to using the #5 rb spot for someone who Belichick is already comfortable with. He seems a perfect one year transition to the rookies.
BOTTOM LINE
Belichick is the best in the league in getting value from the players zat the bottom of the roster. Morris as the #5 running back shows that.