It appears that they do talk to each other:
This works: https://aussie.zone/u/Zarobi@quokk.au
but this doesn’t, and I don’t know why: https://quokk.au/u/Zarobi@aussie.zone
I don’t know why that doesn’t work when this does: https://quokk.au/u/davel@lemmy.ml
Perhaps it’s because none of your Zarobi@aussie.zone comments or posts have ever federated to quokk.au, so quokk.au isn’t aware of user Zarobi@aussie.zone’s existence yet. You could try subscribing to or commenting in a quokk.au community; maybe that would “prime the pump.”