>>> waiting for the snapshot to be removed…
Where do you see a stuck task? Only in the backup application, or also on the ESXi host? Maybe it's just a communication issue where the snapshot removal failed, and the backup application is still waiting for feedback!? If the task doesn't show up on the host (i.e. connected to the host directly) anymore, then it most likely doesn't run anymore, and you should be able to manually "Delete" the snapshot from the Snapshot Manager. If no snapshot shows up in the Snapshot Manager, create a new one and then run "Delete All".
One thing you should check is whether there's free disk space on the datastore, because the second/new snapshot will grow until deleting the snapshots has finished.
Remove Snapshot is showing up in the VI Client, attached directly to the host. The datastore is showing 299GB free space, so I'm ok for now on that end… I think. The growth rate isn't super big at present but I'm getting a little nervous that it's not going the other direction.
In the process of creating and deleting snapshot Veeam plays only "requester" role, which means it just issues a certain API calls to vCenter/ESX(i) hosts. So, I would exclude Veeam from this equation, and try to understand why the underlying host can't cope with snapshot removal operation. If possible, I would open a ticket with VMware.