some interpretations of prophecy say that the many headed beast that is non-denominational groups will unite with Islam -- after all they (the non-denoms) have moved away from orthodoxy and some have even started rejecting the Trinity etc. as they move farther and farther away.
Only those groups that reject Jesus Christ as Lord, God and Savior will be the many-headed beast -- that will not include Catholics/Orthodox or the "Christ is God" believing non-Catholics