It's really not the way you are supposed to do it, but you can try it. The water in the pipe facing upwards will definitely freeze; whether that will do damage is unknown. I don't think anyone really knows for sure what will happen to main drains if left "un-blown". In theory the maindrain line that runs above ground or near the surface will freeze and as that pipe extends into the ground the water won't be cold enough to freeze. So the expanding ice should push on the water going into the ground forcing the water pressure out the maindrain. Really who knows what happens in real life until they make a pool with a visible maindrain and you can actually watch what happens. I know in plumbing they say pressure from the water will crack a frozen pipe and not the ice itself from expansion. I'd be worried that freezing ice in the pipe could get hung up in a section and end up freezing and cracking the pipe before the excess pressure has a chance to exit through the maindrain. I could be totally wrong on this though, I think you still have to factor in if the maindrain line starts to freeze near the pad and pressure wants go towards the path of least resistance will it be the maindrain in the bottom of the pool? Keep in mind that there is a lot of pressure at the bottom of the pool pushing back on that expanding ice; maybe this is how things get damaged.
Regardless, maindrains on above grounds are about the only time I saw a maindrain actually be useful. It seems in a round pool you can direct the return line to cause the water to sprial in the pool and this causes any sinking debris to end up right in the center of the pool, right where the maindrain is at. It's almost self cleaning.