They'd primarily use him as a return only guy and my guess is they trusted Crowder more fielding punts in Prime Time on opening night in LA than a rookie. Look what happened to Cook despite fumbles not being a problem in college.
I also think they like Kumerow as a WR more than most of us do. Especially as a blocker. To quote the insufferable Aaron Rodgers, “I love his reliability. I think he’s a fantastic, steady player who’s very heady on the field. He makes plays, he plays with a lot of confidence and he’s a guy you love having on the squad." My guess is McDermott and staff see him the same way.
Crowder can also line up on the outside if need be but I still think Shakir is your best third option so I was a little surprised he wasn't activated last night. Maybe he will be next week or maybe we're all idiots who think more of him than the current coaching staff.