It is possible to display Whatsapp messages on the watch. There is and is no app for Whatsapp on the watch. This is controlled via the Gear Manager app.

WhatsApp messages are displayed as notifications and you can even reply to them. Unfortunately, there is no dedicated app. Old messages cannot be displayed and completely new ones cannot be created - only replies to displayed ones. But that's ok for me - even if a dedicated app would of course be very desirable.