Can Survey123 use existing data from Collector? We'd like to use Survey123 to create new tables for our existing points on the map.
I assume you mean new records in existing tables (not new tables)? If so, yes this is possible - Survey123 supports the editing of records in related tables.
Editing data: Prepare for editing existing survey data—Survey123 for ArcGIS | ArcGIS
Using your own data: Use Survey123 with existing feature services—Survey123 for ArcGIS | ArcGIS
We already have a point layer with points recorded on the map. Can we use survey123 to access those existing points and create new related tables?
Jordan, take a look at the links provided in the first response as the answer is "yes"; we use this methodology for some of our surveys. You'll just have to do some footwork to get a full understanding as to how things work and I would highly recommend using a test dataset until you get the process hammered out.
I would recommend looking into the Inbox and creating a survey that has your geopoint question as a read-only; unless you want the ability for it to be updated by the survey.
Retrieving data ...