Why not? I was under the impression that the reason that he 'officially' came back from his loan over the two weeks that included the International break was so that he was available for the play offs if they didn't play us. Is this not the case?
Being on loan doesn't preclude you from playing in the play offs, or Watford would be utterly stuffed.
Being on loan to Palace from the Albion stops Dobbie playing against us. If the unthinkable were to happen, he'd be available for the final.