Looks like the Terms of Service hadn't been updated for Unite, but that has been fixed now.
There was some confusion about the part that talked about "uploading content to Opera's site", and people were worried that using Unite would mean that Opera owns all your data. With Unite, you aren't uploading your data to anyone's site, but I can understand why people got confused.
So now, the Terms of Service explicitly mention Opera Unite:
For the avoidance of doubt, this clause does not apply to the files you share as an End-User of the Opera Unite, as such files are never uploaded to Opera’s site. Opera will not make a claim to own or use those files.
That should hopefully people's minds at ease.
Remember that with Unite, you are in control of your own data.