Webhooks are probably the best approach for this type of thing, but an alternative would be to use a ArcGIS Online Notebook that scans your service for new emails at intervals using Python, for example every 15 minutes or every 30 minutes.
You'd want to create a feature service that has a table where you keep the last known count of surveys. When the script runs, check your current count against the old count and send an email that indicates how many new surveys have been submitted. After doing so, update your table's count.
If you'll be deleting surveys, you'll want to enable edit tracking, store a "last checked" timestamp rather than a count, and scan for records that are newer than your last timestamp.
As an alternative to a single email, you could send one email for each new record you find.
The main downside of this approach is the delay between submission and notification, however the delay will be at most 15 minutes, if that's how you configure your notebook.