Not at all, it is an effectless Ritual Monster.

Gem-Knight Pearl is an effectless XYZ monster.

The third gym is Fantina's gym and she has ghost Pokemon. As long as you have a Pokemon with bite or crunch, it should do okay. Otherwise, you could just use a Staravia. Since it is part normal type, all ghost type moves are effectless. One thing to look out for is curse. It will take out 1/4 of your max hp EVERY TURN! Bibarel might do good.

No, they would become effectless Effect Monsters.

That's because Gemini Monsters are Effect Monsters who have a continuous effect that makes them be counted as a Normal Monster while on the field. If Skill Drain is active, this effect is negated, and the Gemini Monster reverts to being an effect monster. However it does not gain its effect monster abilities, these are only switched on by a 'second summon' of the Gemini Monster.