The biggest problem I see with your suggestion is that it posits a conspiracy where none need exist, particularly that early in the Covenant.

What we know of the Huragok, as of Contact Harvest, is that they were Forerunner mechanics who were good at fixing things, but didn't do a lot in the way of leaving documentation. You can use a Huragok to repair stuff, maybe even build something new, but it's difficult to analyze something with them. That's what the Prophets were trying to do on the Dreadnought: analyze and understand how the machinery works.

In addition, the Dreadnought was a Forerunner warship. The technology on it may have been 'sensitive', and security measures prevented any Huragok that wasn't approved from working on the ship.