Backup files - Are they safe to delete?
I can't speak to 'via an AWS CLI script' specifically. But SQL does not care where the backups are.  It knows they got taken and where they were written to.  

Assuming you are using a system wide backup product like TSM to backup your SQL backups as well as the rest of the machine:

Don't delete the fulls and diffs, overwrite them.

If you run your full and/or differential backups at 6AM and you backup them up remotely at noon.  You can safely overwrite them at 6AM the next day.

You can delete the local t-logs when they are at the remote location.  You might want to leave 24-48 hours of them locally for "accident" (someone did something stupid) recovery.

It is important that ensure that your SQL backups are completed before the the remote (i.e. TSM) backup process runs.  You create SQL backups, because products like TSM will not backup files in use, like your mdf &amp; ldf files.  It will also not backup, your SQL backups if they are being written to during the off site backup.  I ran a 7 week experiment appending backup files, and TSM did not move the backups of site until the experiment ended.


  Off site backups, It looks like my offsite backup solution (IBM Spectrum) is not backing up the trn file. I suspect this is because the file is constantly being edited. Source 


Besure to regularly validate your backup solution with restores from your offsite location.