I have tested this feature on my mac.
if you add any files to shared dropbox folder, the file or folder gets synced on the mac side. Yes, you would not get the dropbox features such as send email, share links etc in windows if you make use of shared folder features . But those things one can perform on the Mac side itself once the file is saved.
The main purpose of uploading the file to dropbox server will still be served by making use of shared folder feature.
I have not tried installing dropbox on windows side. But ideally if you install Dropbox on Windows and point it to the shared dropbox folder in windows itself( network location in windows ), you should be able to take advantage of all the features.