Reading your use-case, it isn't that easy to achieve what you want to do... Unless:
1. Make backups of the endpoints to a Veeam Backup & Replication repository locally.
2. Then make a backup copy job to your repository (as a cloud provider (cloud connect) seems like the best way to avoid VPN's and trusts and those kind of things...). I assume here that those different organizations are your customers?
If there are VPN's and such in place, you can do the same but then without the cloud connect part, just a backup copy job to your repository)
However, keep in mind that a few things won't work today:
- Testing of the backups (this will be still a manual job, surebackup isn't supported today)
- The rollup of the backups happens for you (we are using forever incremental)
So, depending on your business model, Veeam Cloud Connect could be a solution for you