Yes, I do because ideally the tubs should fit very tightly. The rack I bought (home made by someone else) originally had lidless tubs that didn't fit tightly. After a couple of escapees, I had to put aluminum foil over each tub (really hard to keep it intact when feeding). Now I have tight-fitting tubs and need the side holes for ventilation.
I built all my own racks and used a 1/8" thick piece of melamine board as a spacer between each tub and the next shelf in line, so there is not enough room for escapes and plenty of ventilation so there is no need for more holes.
i do have holes in mine, but honestly it depends on how tight the fit is (top to bottom) and your personal preferences. i noticed even with holes that sometimes i get a little bit of condensation by the water bowls...and leopards require a pretty low ambient humidity, so airflow is pretty important. if there was an 1/8th inch gap, i would say that should suffice, anything more would leave escape possibilities.