No, it is not possible to hide drives on Explorer tab of the File Tree View of UE v17.00. But you can hide all drives you don't need currently by right clicking on a directory and selecting Set Directory as Root. With right clicking later on this directory again (now always at top) and left clicking on Restore Default Root you can restore the view to see again all drives.
There are several configuration settings for the Explorer tab of File Tree View. Open Advanced - Configuration - Application Layout - File Tree View. Unchecking the settings Show volume labels in Explorer view and Scan for empty folders in Explorer view prevents accessing all drives on initial open. Unchecking Show registered file type icons in Explorer view makes loading the directory lists much faster.
BTW: If you never or only rarely need that drives you can disable those hardware components in bios of your Dell computer or in device manager of Windows. That would also save some system resources and results in less power consumption.