My best guess would be that because when combining the offspring gains techs based on the parents', that it's potentially possible to learn if one parent has the analogous tech. I've never tried though, so I can't vouch for it being possible. Most of my experience is also with the first game, so I'm not an expert in how it works in other games.

That's actually what I was thinking; getting a monster and learning many many techniques with it before combining it in such a way that a Kato is what comes out of the combination that starts with Oil fire. This seems viable as when I used a gameshark to just unlock the technique, I could get it again via combination, so it wouldn't re-lock it. It's worth some attempts.