This should work, it did definitely work for me. Maybe the hierarchy matters?
My setup was:
animated dummy helper > dummy > camera
> dummy > geometry
So both the geometry and the camera were linked to the animated dummy respectively.
If it doesn't work, make sure to set up a simple repro case for support.
Also, something I discovered recently: if you are using distance maps for mapping, these will not animate with object motion blur, only camera blur. So in a setup like yours, if the moving object would use distance map, the textures from the distance map would get motion blur when they actually shouldn't.