D5300 raw support started with LR 5.3, so LR 6 should be ok.
What does “not recognize” mean? Are you trying to use tethered shooting, or download files from it after connecting a USB cable to the camera, or trying to download raw files from the memory card after putting the memory card in a card reader, or what?
If you’ve transferred or viewed the NEF files with any older Nikon software, it’ll corrupt the NEFs so Adobe software doesn’t recognize them. A way to test would be to try transferring photos from the card to the computer without using Nikon software and see if things work any better. If so, you can correct the corruption of the photos that you cannot just retransfer using a utility from this website:
I am trying to shoot tethered. I keep getting no camera detected. I just downloaded digicam and it can tether to the camera.
I ended up going into device manager and deleting the drivers for the Nikon d5300. I rebooted and then reinstalled the device. It appears to now work, though I have to wait about 20 seconds for my computer to find the camera.