I haven’t implemented @mscottveach’s two-machine approach, but something similar. I run Windows 7 in a VMWare machine and put files into folder(s) that are indexed in DEVONthink and accessible to Windows. (This really has nothing to do with WIndows - since DEVONthink can index any folder regardless of what app is accessing it.)
Is that “sharing data easily”? Depends on what’s “easy”, but it does work.
Email – look, for example, at this thread.
FTP – though DEVONthink doesn’t run an FTP service, your Mac certainly can. And then you’d put the files into a folder indexed by DEVONthink, and we’re back to the beginning …