Yes, just Ultima. In a way Ultima and Zodiac are the FFT Blue Magic, which is traditionally learned from enemies.

The tricky part about teaching Zodiac is that you can't cast it on allies. You have to get in a fight against a summoner, lower their Faith, then hit them with Zodiac so they learn it.

You have two options at this point:

1) Wait until they cast Zodiac on your summoner.

2) Kill them and there's a 50/50 chance they'll turn into a crystal when they die. You can learn Zodiac when you run over the crystal.

I haven't tried method #1, but method #2 works well if you're patient. One combination of random encounters in Terminate in Deep Dungeon includes two summoners. Good luck!