If the affected creature gains an ability after Ovinize resolves, it will keep that ability.

Ovinize overwrites all previous effects that set the creature’s base power and toughness to specific values. Any power- or toughness-setting effects that start to apply after Ovinize resolves will overwrite this effect.

Effects that modify a creature’s power and/or toughness without setting them to specific values will apply to the creature no matter when those effects began. The same is true for counters that change the creature’s power and/or toughness.