Short answer: no, Echoes does not require access to the codebase! The long answer however depends on your source control manager.
You can give members of your organization access to Echoes at no extra cost.
Echoes reports require day-to-day efforts to be tagged with their intent. This is typically as simple as adding labels to GitHub pull requests or GitLab merge requests, and there are multiple ways in which Echoes makes this task even easier.