I'm building small karts for my grandkids & I'm using pocket bike brakes...
There are just about no bicycle parts that can be used on a go kart...
I wouldn't say it is a definite no. Mountain bike disc brakes have to provide a LOT of braking torque to compensate for the disproportionately large wheel diameter to rotor diameter ratio. And they can do that with perhaps a 200# rider going down a 100% grade.
What they are not meant to do is grab down on a disc that is spinning 1000 rpm, so pad life could be adversely affected.
On a yard kart that does 25mph and weighs a couple hundred lbs with rider, and having brakes on the axle AND front wheels, they would probably be just fine.
Biggest problem I could see is mounting. By the time you figure that out and buy or make the parts, you could have gotten a complete mechanical disc brake kit that is designed for go karts from gps for 60 bucks.