Did some more research. It looks like if you get invited to a group in WU you can read the messages from the group creator that is using android or ios. But messages from other android or ios users are not showing in WU.

update:
Looks it is working random? In an other new group we see the messages from all WA users. Excisting groups I see no message from WA users and some groups only see the messages of the WA group creator.