Sure. Any incidental effect related to the actual physics used to encode information potentially could leak information. Fluid has mass, and accelerations require forces, so acoustic, acceleration, and thermal side channels are all a possibility.

Absolutely. In order for fluidic devices to function you have to vent fluid to ground. For pneumatic devices this is typically the surrounding air. This should produce an acoustic signal that can be detected. However, one could operate such a system in a closed loop manner to prevent this where in all the ground vents feed back into the pump supplying the circuits. However, there are still likely to be load variations that could be detected.