I tried simulating a similar setup with and without a 8mm hole on the side, with a 100lb load from the tip of the handlebar (20 degrees front back and 20 degrees left right). I see very little difference?
With hole: (There is high stress on the FRAME near the clamp… happens on some of my simulations, but not sure if it’s “real” or not.)
Just from my experience with breaking seatposts, that’s not the place where they typically fail, and I personally wouldn’t worry about it. Fairly low stress area (as your simulations confirm), fairly minor dent, I don’t see any reason why it should fail significantly faster than a normal one.
Maybe keep an eye on it and check for cracks occasionally (which is a good habit anyway). I’ve pretty much never been surprised by a suddenly broken seatpost, they usually get a bit creaky or feeling soft with visible cracks before ultimate failure.
There is a thread on here with many pictures of broken seat posts and most break near the top where the four bolt mount is welded on. I’d link the thread but can’t seem to figure that out at the moment.