@dbuscaglia, sure, S3 Loader is just another consumer/subscriber. As long as all the consumers are working OK (and respect each other) that should not cause any problem.
The diagrams in this post show multiple consumers including Redshift load with Lambda architecture.
Here’s some guide that explains handling consumers issue that could clarify this more: https://docs.aws.amazon.com/streams/latest/dev/troubleshooting-consumers.html#consumer-app-reading-slower.