Well, I personally think that Bosch probably knew. But the Colossus and the installation were probably extremely heavily defended. Remember, this was the flagship of the GTVA, and the biggest joint venture between terrans and vasudans, so they would have put everyone and their mother defending it who weren't committed to other parts of space. With the size and amount of people actually working on it, it wouldn't have been a secret for too long. It just would have been too much of a hassle to actually do anything about it.
Plus, guys, the cut scene and the game doens't say anywhere that it was never attacked or never had an attempted sabotage. You never know, maybe there were attempts to take out the installation, and maybe even Bosch tried to impede construction.
Would be a great campagin, actually... You're committed to defend the Colossus and the installation while construction... Watch those transports that are coming... they could be loaded with high-yielding explosives...