You can but just because you can do something, it doesn't make it a good idea.
I have successfully co-authored with another but we were in very different time zones. That worked just fine using Dropbox and I believe Google Drive also works OK. The one to avoid is OneDrive. I experienced problems and others have reported the same on these forums.
If you are simply working on different topics, that should be OK. What will give grief is things like two or more working on the TOC, editing the skin and suchlike, more than one person working on the same thing.
It's down to discipline. Ideally you should be using source control as those tools have mechanisms to protect you.