No, that's wrong, the only way an initial overvaluation hurts pre-IPO investors is if the stock gets delisted, or the market is so offended that it starts caring and undervalues the company. Otherwise, employees are just fine; Since the market doesn't care, it gives them fair value when they have a chance to sell. They lose out on cashing out during the over-valuation period, but that was just free money for those that pulled the strings, pre-IPO investors and Facebook management that could sell at IPO
The only people hurt by the initial overvaluation were the people that bought high. Everybody else wins or is neutral. Everybody. Again, unless the market starts caring about retribution and undervalues them. Otherwise everybody gets exactly what the market will give them.
The ibanks, Zuckerburg, and initial investors that sold on IPO day or shortly after, all win by a huge margin. They pulled the wool over lots of people's eyes; perhaps not intentionally, perhaps they honestly believed their own bullshit, but in any case their irrational exuberance hurt them not one bit.