Some folks are indeed using Aurora with SpiceDB, but I don't think any one from Authzed has exhaustively tested it. The recommendation around PG/MySQL for regional deployments is mostly under the assumption of the typical replication models for these databases (e.g. read replicas). I'm not familiar with how Aurora does replication/scaling across regions, but datastores like CockroachDB or Spanner operate with awareness to regionality, so that's why we recommend them.
It looks like there is still regional replication lag, so you can consider Aurora to be a similar experience to manually scaling out a regular Postgres/MySQL to multiple regions with the typical replication delay.
If there are things we can add to the Postgres or MySQL datastores in SpiceDB to improve consistency on Aurora, we're definitely game for supporting it. Just file an issue if you find something.