So yeah, its possible but Samsung doesnt want to work on it. There are rumors that say Samsung wont launch any other watch with Tizen in it, maybe they are planing to abandon us...
I noticed that if only one photo arrives, it is not seen, but if more than 5 photos arrive, only one photo is seen on the screen of the watch active 2, the other ones are not .. but one is seen ..
With the latest update Whatsapp photo's are shown on the watch. It doesn't show on the notification itself, but does show when you swipe to your notifications after. You may need to wait a couple of seconds for it to load if you're too fast.
You may want to check if you have set "auto download photos/images" in WhatsApp app. If image is not automatically downloaded in the phone app, only the camera icon will be shown.
This is from what I have learned from changing the settings in WhatsApp.