I think an easier option would be to use the default SSI configuration for the RS507 and a Datawedge intent to receive the data in the app - this is detailed at this link: Data Capture Intents Tutorial - Zebra Technologies TechDocs
You would not gain any advantage using the 507 in serial mode but the implementation would be significantly more complex.
The advantage of using the scanner in serial mode is that you are able to use either the built-in scanner or the RS507 scanner independently.
If you use the SSI mode the RS507 will be set as default and the built-in scanner will be disabled.
We actually had some customers asking for this and we had to develop our own application for solving this.