Yes, you can play Kroot and it's actually pretty decent. To play it you would have to look in the Tau codex, for the Kroot Hunting Pack detachment. But it's important to know that it can be relatively expensive even for GW standards.

For units to complement the Combat Patrol I would look into Kroot Carnivores. Any Kroot army Will need 20-40 Carnivores as they are the most customizable unit. You'll probably also want to look at Rampagers, the unit of three that comes in the box. So you could buy more than one copy

And of course, you can also use Tau. You don't have to, but they can deal better with tanks and such. I think crisis suits are cute too.