Vanaspati Ghee is never offered to God at the time of Aarti in the Diya or to the dead body at the time of cremation. Only pure ghee is offered.
It is considered a bad omen to offer Vanaspati ghee at the time of the cremation ritual even though the consciousness has left the body.

What is not offered to God should not be offered to our consciousness and that was the reason for this ritual in a temple. Vanaspati ghee increases bad cholesterol and reduces level of good cholesterol in the blood. On the other hand, pure ghee only increases bad cholesterol but does not reduce the level of good cholesterol. The medical recommendation is that one should not take more than 15 ml of oil, ghee, butter or maximum ½ kg in one month.

It is a spiritual crime to offer vanaspati ghee to God.