I think the question is:
If a creature with the Rooted trait also has the Uproot trait, and if the mana were paid to Uproot it and if there were already an attached hidden enchantment, that was reveal after the creature was uprooted but before the end of its action phase, could it gain the Flying trait?
Uproot X (Object Trait)
This creature can uproot itself from the ground and move freely. When this creature is activated, you may pay X mana. If you do, it loses the Rooted trait until the end of its Action Phase.
The way I read this trait the answer is yes, now intent that is something totally different...