As Neetu says above, yes, you can do that. In case of SAP, you will likely need the SAP Connector, which is a different product and has an independent license from QlikView.
You can organize your script in tabs. So you can create one tab for SAP extraction, another tab for Excel extraction, another for Oracle... If you save all these sources into QVD files, you can easily use them later to build a fact table.