No, the dust cover is the rubber end seal on the piston, That's clearly got a gasket where the wheel cylinder mounts to the back plate. You could easily make some out of gasket paper of a heavy gauge but to be honest clean the areas down and use a little silicone (mastic type). I can't see that its there for any other reason than to prevent rusting of the backplate edges/cylinder body. Not now used on modern applications.
