Vegetable ghee is utterly pointless; it has no particular taste, and just solifies as your curry cools down, making it look horrible. Don't bother with it.
Butter ghee is used in most BIRs melted on nan breads. It is used in dished like 'butter chicken', etc. There seems to be an idea amongst the great unwashed that BIRs use it extensively, but this is nonsense. I've only ever been to one BIR where it had been used for oil (in a madras). It was digusting. I hate ghee, and would not eat BIR food if it was used. Furthermore, I am allergic to cows milk anyway, so I wouldn't be able to eat BIR food if they used ghee.
Just stick to rapseed or sunflower oil.