Hi Joseph,
I assumed that you want to add features directly from the code without changing the feature server behind.
In this case, I am not positive that you can add any existed features or create a new category feature from the code behind.
Put another way, even though you can add the feature but you can't fully function the vote button, because the vote information will only update those features connect with the table behind. Like the description said in the example:
When you "click to vote", the "voteRecordAttributes" are populated; specifically the "sf_311_serviceoid" attribute is set to the "objectid" of the selected feature. These attributes are then included in the "voteRecord" graphic that is then saved through the feature layer "incidentVoteTable" using the apply edits method. Each time you vote a new record is added to the "Incident Priority" table.
1. Make sure the new feature/category you add in your feature server
2. Create the relationships both in ServiceRequest_IncidentPriority to Incident Priority and IncidentPriority_ServiceRequest
Hope my tips may help you.