Yes, DISKETTE is a Scrabble word!

Letter values in Scrabble US: D 2, I 1, S 1, K 5, E 1, T 1, T 1, E 1.

Is it a valid word?

DISKETTE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a small plastic magnetic disk enclosed in a stiff envelope with a radial slit; used to store data or programs for a microcomputer

Also: floppy disk.