It might be possible to disguise the numbers, but not easy at all. The main reason Israel completely failed to notice the 1973 assault was because Sadat was not Nasser, and they didn't believe he had the intent or the determination to fight a new war.. Thus they completely ignored all signs of a military buildup until the Egyptians broke through the Bar Lev line. Had Nasser been alive in 1973, it could have ended differently.
Hell if Nasser decided to not block the traits and expel the UN force Israel may not know about the military buildup. Of course Nasser could disguise this, but yet again this is before the 1967 war gave Israel too much overconfidence that got shattered by the Arab states in 1973.