The following is quick summary of both the Office Upload Centre and the OneDrive for Business Synch Client and a discussion of why is it safe to have them both running simultaneously.
Office Upload Centre
Upload Centre manages the offline cache when SharePoint documents are opened in the appropriate client application. By integrating with Office it enables co-authoring and some other ‘integration’ features such as sharing from the Office client applications and ensures that changes are synched back to SharePoint even if the connection is lost.
OneDrive for Business Synch Client
OneDrive synch ensures that OneDrive documents which have been synchronised to a local folder remain the same (synchronised). It also acts as the synch client which is used for the synchronisation of other SharePoint content such as a Document Library in team site. It does not integrate directly with Office applications. NOTE: Microsoft are upgrading the synch engine to improve reliability but only for OneDrive (but it is probably safe to assume that it will reach the rest of SharePoint eventually).
When do they meet?
The closest these features get to interacting with one another is when a document stored in OneDrive is opened in the client application. In this scenario it is Upload Centre that will ensure changes are persisted to the document. Once this occurs it is OneDrive Synch that ensures that this change is replicated to the synchronised copy stored locally. If the document is edited in another way then Upload Centre will not be involved.
Both products are a core part of the Microsoft cloud suite and although you can disable them, you can also be confident that they will work together.