I wouldn't worry about using deck screws on an aquarium stand. MAYBE the hood, but even then, I don't think its necessary.
I built a deck on my house a few years ago with Phillips deck screws, I recently re-did a portion of the deck to put in a hot tub, and to my dismay, most of the screws I took out had started to rust on the threads. It looked like the coating came off while the screw was being screwed in (I pre-drilled every hole, too). These were the nice name brand screws with an thick, tough looking coat, and I was using treated pine. Not some fancy hardwood or composite or anything.
I replaced them with stainless steel deck screws. But usually I just use drywal screws + wood glue for aquarium related stuff.