As per currently known API importing issues, $ref pointers from the OpenAPI specification can't reference external files. However, it could be a crucial feature to standardize APIs across an organization. As is we can certainly make it a local reference but it enforces duplication and becomes difficult to manage length OpenAPI documents. Hence please allow to import OpenAPI documents with remote references.

Known import issue reference: https://docs.microsoft.com/en-us/azure/api-management/api-management-api-import-restrictions