No, despite all of the documentation saying that it is "mandatory" and "required", the NSTableView.h header file says:
This method is required for the "Cell Based" TableView, and is optional for the "View Based" TableView.
If you implement -tableView:viewForTableColumn:row:
to do all the necessary work to display your data, you don't need to implement the other method.
The header file also says why you might implement it for view-based tables:
If implemented in the latter case, the value will be set to the view at a given row/column if the view responds to -setObjectValue: (such as NSControl and NSTableCellView).
This doesn't seem any easier than just implementing it in the normal view-based method, though, so it seems more like an upgrade-compatibility feature than something you'd actually want to use in a new application.