To determine whether the target creature gets +3/+0, look at its creature types after you've gained control of it, untapped it, and given it haste. If it's not a Goat at this time, it won't get +3/+0, even if it becomes a Goat later in the turn. If it is a Goat, it gets +3/+0, even if it stops being a Goat later in the turn.