Hi Leporine, the jam rules apply only to the actual VN, not its website or any extra materials (see also above crystal's question about the itch cover which follows the same principle).
A game page that features a decorative banner with people not shown in the game should be fine, but just try as best you can to make sure the player who only plays the plain game without this context has a full experience. For example if you have a romantic game where only the Love Interest is shown as the sprite and the game is narrated by the Protagonist, then an itch banner that shows their faces inside a heart shape is fine.