Two Emcees are better than one at the Jan. 13 opening night party for Wrong Moutain. Pictured are Joel Grey, who created the Cabaret character, and the Tony Award winning star of the recent revival, Alan Cumming. At right, Victor Garber, who recently portrayed Daddy Warbucks in Disney's TV "Annie." Wrong Moutain, an often savage look at the American theatre, concerns a bitter middle-aged poet who bets his ex-wife's new husband, a wildly successful Broadway playwright, he can write a smash play - and does. Mountain, by David Hirson of La Bete and starring Ron Rifkin, performs at the Eugene O'Neill Theatre.