Samsung does sell a USB host adapter, but the Galaxy Tab line is notably absent from the compatibility page. I have not had any luck with any OTG cables on my SGN tablets. You could try one of the USB OTG checker apps to make sure on the NGTS, but my SGN 10.1 2014 shows that the USB OTG signal is not detected. Ditto for my SG S5 phone. It's odd because older Samsungs supported it.
On stock firmware, I'm not sure you'll ever see OTG support. I'd love to be wrong, but I haven't found a solution yet.
OTG cable works perfect with my Galaxy S5 so I bought a cable online for the tab 4 but it doesn't see the flash drive. Would have been sweet! Wonder if the problem is hardware or OS.