Works as intended: helper applications open (they don't without this patch unless you install symlinks in system directories) and items can be opened via the Mac GUI. For folders this is limited to dragging them onto the Dolphin application icon (in a folder or the one in the Dock); I'm not aware of a way to indicate that these should be opened preferentially by Dolphin.
Opening folders in individual windows and thus in multiple application instances means you get as many Dolphin icons in the Dock and AppSwitcher. I don't think anything can be done against that, other than adding MDI support to dolphin.
Dragging files and folders from the Finder into a Dolphin window already works as it does on Linux. The reverse operation works too but only for the `file:/` protocol.