Yes, starting with version 1.0.95 Sync features one-way synchronization. It is established via read only permission (formerly known as key or secret). Any folder with a read-only permission will be fully synced, but changes made in this folder will not be synced back.
To establish such a one-way connection, use the "Read Only" permission while sharing a folder (available for both Standard and Advanced).
HOW IT WORKS
RO peers can only read data in a shared folder, therefore if you update (add, delete or modify) files on RO peers, these changes will not be synced to others. Should a peer with RO permission make an attempt to update some file, all synchronisation for this file will be stopped. Meanwhile, Read & Write (RW) peers will be indicating that they are trying to upload the files that were changed by the RO peer.
To prevent unintended file changes leading to synchronisation break-offs, RO folders have the option 'Overwrite any changed files'. If enabled, Sync will do the following:
1) renamed file in an RO folder will remain there. Besides, the same file with an older name will be re-downloaded
2) deleted file will be restored
3) edited file (changed content) will revert to the most recent version supplied by a RW peer
4) added file will not be deleted, nor will it be synced.
Technically, RO peers can transfer unmodified files to other peers. This is due to the nature of P2P protocol and may happen when the files received by a RO peer from a RW peer have been requested by a new peer which has just connected to the folder.
Remember that in case of data backup (backup makes use of RO folders), deleting files on your mobile device will NOT delete them on the backup device.