I checked with a friend who's supposed to know about these things (he's written an unpublished sci-fi guide called "Vintage Science Fiction") and he says that, yes, the co-billed feature was "Earth vs the Flying Saucers".

I saw "Earth vs the Flying Saucers" when it first came out, and I remember seing "The Werewolf", too. I remember vividly seeing "The Werewolf at a drive-in theatre when I was ten years old, so I guess I saw "Earth vs the Flying Saucers" the same night, at the same drive-in.

What a night for a wide-eyed, ten-year-old, sci-fi buff, eh? Now there's a memory I'd love to resurrect with hypnosis!