No, they do not own them. They are the official importer into the US. Walther used to use Interarms. Now they use S&W. For whatever reason, they don't want to establish their own official presence here in the US, like Sig and Glock have.
S&W builds the PPKs for Walther. And, they also did a few P99s a few years ago, but there was apparently some quality control issues. So, all the P99s are imported from Germany again.
Now, the SW99 and SW990 - Walther makes the frame and S&W makes the slide and barrel.