If the shields were activated within an atmosphere, capturing some of that atmosphere, then moved out into space, the vacuum pull of space on that atmosphere could theoretically create some sort of shield-implosion effect...assuming the shields are weak enough. Seeing that said shields are supposed to block attacks from powerful weapons, it seems unlikely.
BTW: Why shields were not used in the Freespace timeline yet were in Descent timeline: Regeneration. The GX required an actual, external charge to power the shields, whereas in an open-space setting, shields would need to be self-regenerating. It's completely possible that the GTA actually used a similar shielding system on their craft before meeting up with the Shivans, because while a single hit would result in actual armor damage, without protection a single hit could rip through the armor entirely (think of what would happen if the cockpit was hit with a missile). However, the GX relied on shields entirely, whereas the GTA relied on hull armor. Perhaps the system was perfected so that shields were used as an adjunct to armor, and thus the shields acted as a layer of absorbency to weapon fire, allowing minimal impact and energy to be transferred to the hull itself. Therefore, the shield was never actually destroyed. The Shivans developed a wall of regenerating energy around their craft in addition to ordinary shielding, however, meaning that the outside shield could actually absorb ALL of the energy without any energy transfer to the hull.That's my theory.
If there is air inside of the shields, it wouldn't cause an implosion. It'd be an explosion because space is a vacuume and the air must go out.