Usually we read, on reports, aircraft reporting urgency or emergency during the flight, while airborne. But, is it correct to use these "words" on ground?
Yes, it is correct to use MAYDAY or PAN PAN PAN on the ground.
In recurrent training we are often reminded that in the case of a rejected takeoff in a foreign country it is important to use MAYDAY or PAN PAN PAN on the ground to avoid any confusion due to language difficulties.
It's probably a good idea at any airport as a disabled aircraft on a busy runway could be a major hazard to other aircraft landing and taking off.
Absolutely they are correct to use on the ground if the situation warrants. They are used to express an emergency or urgency, and those can happen on the ground as well as the air. Those conditions are roughly the same: passenger illness requiring medical assistance, an engine fire, unlawful interference, etc.
When you make the call you would report your position as being on the ground, and where you are.