A HIT pop show needs a star name, good supporting bill, smooth production, and a dash of glamour. And this is just the forumula promoter Danny Betesh used for HERMAN'S HERMITS' new tour which opened last Thursday at Dover ABC.     Herman is now an old hand at one-nighters and controls his audience as well as many stars twice his age.     He only has to lift his little finger to send the audience into gales of near-hysteria.     The group opened with "Just A Little Bit Better" and followed with "silhouettes," "Listen People" and "Scarlet Ribbons." They also included Norma Tanega's American hit "Walkin' With My Cat Named Dog" before "You Won't Be Leaving and "A Must To Avoid."     The group has improved a lot in the past six months. The Hermits - Keith, Karl, Barry and Lek - are playing better and Herman is developing a strong stage personality.