Would balloons filled with helium still rise in a weightless environment such as a space station in orbit?
No. They rise here on earth because the outside air is heavier then the the helium, which pushes the balloon “up.” Sort of like how a lifejacket will float in water, since it is less dense then the water, thus less heavy so the water pushes it up. Without gravity to pull water or air down in order to push lighter things like a balloon up, the effect becomes null.
A helium baloon rises up in our atmosphere because it is lighter than the other gases. Here lighter means the force of gravity pulls it with less force than the other gases. So in a weightless environment where there is no force of gravity it isnt lighter than anything and nothing is heavier that it. Also without any force there wont be any change in momentum. So the balloon filled with Helium gas if not in motion in an weightless environment it wont rise. But if it has an initial motion (if somebody gave it an impulse) it will move eternally with a constant speed in a straight line.
