I don't see any significant resemblance to Ryan. Anyway, the timing's a bit iffy. The book's publication date was August 1996, which means the cover art was probably done months earlier. And Dark Skies
didn't premiere until September 1996. So would promotional photos from the show have been available early enough for the cover artist to see them? It's possible, but I'm not sure it's likely.
Also, I think the face that reminds you of J.T. Walsh is meant to be Jimmy Hoffa. There is a resemblance between them.