Much of the goal of SlickStack is to reduce bloat in the WordPress stack. Backup plugins tend to be one of the worst contributors to bloat because they not only use lots of CPU and RAM but also save many unsafe archives of data on your local server folders, meaning a security issue too.
Our default plugin blacklist (blacklist.txt) will disallow most any type of backup plugin that is not performing a simple one-time import/export function. However you can use a custom blacklist.txt file if you want to build your own SlickStack configuration.
Backups work much better at the server-level. That is why we have a ss-dump script that runs regularly to ensure your database is safely backed up (and not in a public directory). This script runs before you do things like ss-update or which might potentially cause data loss.
As far as off-server backups, we don’t have this feature but if you would like us to consider adding it please join our chat room or create an issue on our GitHub repo.