I have to concur. It depends on your particular environment. So long as there is a gap between the lip of the tub and the top of the rack, you'll have a healthy airflow as far as oxygen exchange is concerned. The rest of the equation depends on how your local humidity is. If you live in a dry place...then you may not want holes. If your place is frequently humid, you may need holes to keep it from getting too much.

Personally, I'd try them without holes first and see how it goes. If the humidity stays constantly above 60%, or if you frequently see condensation building up inside the tubs...then I'd pull them out and drill/solder a few holes. Repeat the test and drill more holes if necessary until you get it balanced just right.