But the actual construction would almost certainly be found out because it is just too big, and there are only so many sipyards where such construction could even take place...which we are most certainly monitoring.
So, the answer is no...I do not believe the Varyag is a decoy while they are building others. We will know it when they do...unless they have constructed some huge covered facility that we do not know about...in which case the construction of such a facility itself would be very hard to conceal and would get us poking around...IOW, same result.
I do believe the PLAN may make this Varyag operational as an intial vessle to garner experience while they go about building and commissioning their own at a later date. Either way...it is too valuable and potentially dangerous a target for us to ignore and it would complicate issues in the Taiwan Straits area if it attempted to support any Chinese attack there.
So far then, unless the PRC has rediscovered and megatized the secret that Lamont Cranston learned in the orient, everything concerning this carrier is controllable.