Personally, I wouldn't drill holes in the table. You'll end up with Swiss cheese and be disappointed that no one wants to purchase it from you, when it's time to make room in your shop for something else.
Anyway, here's a couple of possible alternatives. A few months ago, I went to look at a Very nice, old, monster, 22" camel back drill press. The owner was deceased, but he had made up a large round flat plate to fit on top of his pristine condition DP table. The plate was milled and scraped to under .001" flatness. He made slots and drilled holes in this cover plate to hold his work holding fixtures and a couple of sized vices. Iam guessing ever 10 years or so he either reconditioned the plate, or replaced it, as the underlying table was immaculate. Simply amazing to see.
Also you could set up a large C clamp, maybe with a piece of bar stock underneath, on the side of the table. This to create a stop, against which to wedge a vise, or the work itself when drilling. Keeps the work,and/or fixture from turning. Very easy to adjust or remove when it's not needed.
BTW. I sure like the other suggestions and photos about holding the work by bracing a piece of bar stock against the column. Simple and effective! genius!
Glenn