Not if you put enough pressure (appx. the same as in shock - but you have to assume what is current pressure in it) before engaging valve. For example, topeak pump uses such system, you attach the hose, but then you have to turn in needle to engage the valve (some others have similar system as well).
With little practice, I can repeatedly attach/detach shock pump w/o loosing much pressure (maybe 0.5-1 psi per attach, if that).
blcman is right, You are not losing any air from the shock when you disconnect the pump. What you hear is the air that is in the shock pump escaping. The reason you see a small drop in pressure when you reattach the pump is because it takes a small amount of air to refill the hose. You can tell thats what happens because its the same amount of air every time(usually around 5psi). If you were loosing pressure from the shock, it would be a random amount every time.
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