Revindex Task Scheduler runs in the same security sandbox as allowed by your IIS application pool. Any script executed will also operate under the same sandbox security. For instance, the default IIS configuration will only allow you to write to the same folder as your Web site's physical path and not outside of it.
Any script executed will be able to read and write data across the portals. Therefore, it is recommended to allow only super user access to the Revindex Task Scheduler module.
You can also restrict user access to the Task Scheduler module by view, edit and execute permissions from the usual module Settings menu. For example, you may want to allow non-administrator employees to run certain tasks but not have access to view or change your code.