Units that have Gone to Ground cannot fire Overwatch, move, charge or Run and must fire Snap Shots until the end of their next turn (pg38).

Units which have the Fearless or Zealot USR cannot Go to Ground, and if they Go to Ground, and subsequently gain either USR, the effects are immediately cancelled (pg 163 and 174 in mini rulebook).

If I'm reading this correct, if a unit Goes to Ground in the enemies turn, it can then gain Fearless in the following movement phase (by an IC joining the unit for example) and then be able to shoot at full BS etc from that point?