The request is to start xosview in withdrawn state (by that, I mean that the application will start inside Fvwm's panel or pekwm's harbour or Openbox' dock or Fluxbox' slit.
The next xosview (2.X) has an -iconic switch so you can start it in an iconic/withdrawn state.
The requested feature is a property of the other applications. I know for sure fvwm can swallow xosview and display it as one of it's widgets in a task bar. Any other window manager that can swallow an X window should be able to do this too.