Hi Aakash
I think we are guessing here about what holes you are referring to. In structural steel, there are often weld access holes / coping holes cut by thermal means, so it is definitely allowed. For thicker steel, or more hardenable steel, you normally need to apply a pre-heat before doing this operation, and there may be a requirement to grind off a certain amount of material to remove the heat affected zone. Generally you will also be required to grind / dress a flame cut hole, because it is a requirement that the holes are "smooth", without notches. Obviously there may be additional client specification requirements, but keep in mind that many of these holes are not round, so you would generally not be able to only use a drill to make them.
Let us know if this is what you are talking about. Maybe you have something else in mind?
Regards
Niekie