I'm not sure if it's possible to drag and drop a folder onto your unity bar - but you can have the same functionality with a bit of editing.
Edit Nautilus .desktop file
1) In a terminal (ALT+T) type: gedit ~/.local/share/applications/nautilus-home.desktop
2) If this already exists, edit the following line to add your NEWFOLDER shortcut:
X-Ayatana-Desktop-Shortcuts=Videos;Documents;Music;Pictures;Downloads;Dropbox;NEWFOLDER
3) Below X-Ayatana-Desktop-Shortcuts add a new shortcut group:
X-Ayatana-Desktop-Shortcuts=Videos;Documents;Music;Pictures;Downloads;Dropbox;NEWFOLDER
[NEWFOLDER Shortcut Group]
Name=New Folder
Exec=nautilus ~/Documents/newfolder
TargetEnvironment=Unity
Where ~/Documents/newfolder is the location of the shortcut you want to add.
(N.B. if this file doesn't already exist you can use a copy of mine.)
4) Type into Run prompt (ALT+F2): unity --replace
Now when you right click your home folder/nautilus shortcut you will see an extra option for new folder.
Create a new .desktop file for your folder shortcut.
1) Run gedit again: gedit ~/.local/share/applications/folder-shortcut.desktop
2) Fill in the file with a sample as follows:
[Desktop Entry]
Exec=nautilus Documents/newfolder
Version=1.0
Name=New Folder
GenericName=ew Folder
X-GNOME-FullName=ew Folder
Comment=Open New Folder
Icon=/usr/share/pixmaps/gnome-computer.png
StartupNotify=true
Terminal=false
Type=Shortcut
2) Save the file and open the location in nautilus.
3) Drag it onto the unity bar.
4) Right click the new icon and click Keep in Launcher
N.B. you do not need to refresh unity for this one.