It is possible but this may lead to naming issues.
You can reference objects in any schema from the objects in any custom top since all custom database objects will have synonyms in the APPS schema.
Thanks for your response, it would be grateful if you provide Oracle doc id or any reference to setup this.
Thanks in advance.
I don't think there is dedicated note for this setup. You can just follow same steps that you use to register single prod_tops. As there is no one-to-one relation with schema and prod_top you can register your prod_top(custom tops) regardless of schemas.
As Bashar said as long as proper synonyms are created and apps can access these objects you can access objects from any schema