$expand is standard OData query option. It is not listed as not-supported in our docs, so I assume it is supported

When I try the following query using customer-dv deployment

https://rdbms-springboot-dv-demo.apps.cluster-london-966d.london-966d.open.redhat.com/odata/accounts/customer(10)?$format=JSON&$expand=address_customer_fk

I get the following error:
{"error":{"code":"TEIID30504","message":"TEIID30504 sampledb: TEIID31176 Could not convert source column v_0.c_1 AS c_3 to the expected runtime type object[][]"}}