Thanks for contacting Syncfusion support.
Dialog can be dragged outside the drag wrapper based on the content set in dialogAction property of UploadBox. To drag the upload dialog all over the window, you can set content property of dialogAction as body. Please refer to the below given code.
<ej:UploadBox ID="Upload1" SaveUrl="saveFiles.ashx" RemoveUrl="removeFiles.ashx" runat="server" AllowDragAndDrop="true">
<DialogAction Content="body" />
Note: If you wish to drag within certain limit then you can change this content target as any container id based on your scenario.
We have also attached a sample for your reference which can be downloaded from the below given link
Now the dialog can be dragged outside the drag area