Cody, 

If you choose to customize the Survey123 app, this will be your own app, different and separate from the Survey123 app from Esri, but they may behave very similar with differences in functionality or the branding depending on the customization. So, it really depends. Most people still follow the workflow or structure of the Survey123 app, but with added or removed functionalities depending on their needs. 

I know several people who have customized and added "map" to the Survey123 app, with their own business workflows added. One of the cool examples that are shared online is the one that was done by Esri Partners and AppStudio Power Users, Geodecisions, GeoDecisions-PennDOT’s Guide Rail Management App 

Thank you,

Erwin