Official comment
Exclusion is local - it controls syncing to your system, but does not remove the folder from your Syncplicity account.
If you want to remove a folder from Syncplicity completely, you need to use the Syncplicity delete function. There are some nuances to deleting folders, explained in this article:
https://syncplicity.zendesk.com/hc/en-us/articles/201234350
Thank you,
Syncplicity support