Nope.

Contact Harvest, P 382:

"All he had to do was claim that the aliens had set their own world ablaze rather than give the relics up. He wasn't worried that there hadn't actually been any relics, nor was he concerned that every Covenant ship's Luminary would continue to misidentify the aliens as relics every time they came into contact. In fact, he thought, his smile suddenly and deviously sincere, this would only make it easier to track the offending creatures down and wipe them out."

It wouldn't take much for the Heirarchs to twist the truth to suit them. The "Reclaimer" symbol is explicitly mentioned to be an obscure one, and the Heirarchs could simply say that the earlier definition was a mistranslation. It doesn't mean "Reclaimation", it denotes a species marked for death for crimes against the Forerunner.

That wouldn't convince the skeptics on its own, but Truth and his cohorts could claim that it was revealed to them by the Oracle in the Forerunner Dreadnought. After all, the fragment of Mendicant Bias did reveal the true definition to them. It was quite spectacular, too. All of High Charity would have seen the Dreadnought straining to break free of its mountings. If the Heirarchs-to-be emerge from the Dreadnought and say that the Covenant has new marching orders and that the Mute Oracle has broken a 3,500-year vow of silence to deliver this edict, they are going to be listened to.