There is little point in kicking with a slow squad whilst injured. The kicking of a performance swimmer is faster than the normal stroke swim of an average swimmer and can be even faster than the normal stroke of another performance swimmer.
I have heard that some coaches move injured swimmers to slower squads but that really defeats the object.
If either legs or arms are injured swimmers can still either just use arms or just use legs. The butterfly body kick is a very powerful exercise that keeps the body moving and fit for the purpose. Especially when the shoulder is injured you can literally worm your way through the pool like a snake on the sand of the desert.