Yes you can use vinegar to descale and clean your Keurig machine.
I use Vinegar in my Keurig every few months to keep the Keurig cleaned and descaled and it works great although you can also buy some coffee maker cleaner solution.
But plain vinegar in the Keruig or any other coffee machine works great.
To clean your Keurig machine with vinegar fill the water reservoir halfway with vinegar and halfway with water and then run the Keurig machine through it's normal cycle like you would when making coffee.
To clean a regular coffee maker that way as well just fill the machine halfway with vinegar and halfway with water or you can just add some vinegar directly without diluting if the coffee machine is really dirty.
Straight vinegar won't hurt it but you'll need to run more water through the Keurig or regular coffee machine to get rid of the vinegar taste.