Vulpix learning moves in very weird orders.

[Courtesy 0]

My vulpix never learned Flame Burst, and learned Hex at level 26 even though it's supposed to learn that at level 28.

It got Will-o-whisp at level 20 instead of 26 too. Everything is kinda wonky, and it's -seriously- bad when you're using a pokemon because you know what it's move layout can be, and you're grinding it up to use against a gym.

Is this intended? Based on when it's learning these skills, there is no Gen skill setup it's following.

[Qaaz 4]

Check this http://serebii.net/pokedex-xy/037.shtml

Reborn is up to date to ORAS level up anchor

[laggless01 51]

The moves pokemon learn by leveling-up are changed to ORAS-system, what you expected is the system in XY.
Check serebii under the ORAS-level-up for your troubles.

[Courtesy 0]

Ah, alright. So Vulpix at level 28 is what I need for this gym then

I'm planning to use Flameburst to terminate both Crobat and the Toxic Mist field, since its one of the skills that auto-kills both pokemon and the field.

[laggless01 51]

If you just want to get rid of the field, gust will do, too. It's understandable to get rid of crobat in such a way, however.
Personally, I didn't have too much trouble with crobat, it always got 2HKO'd by my psychic-type (gardevoir before gen6, gothorita else), but that mist field made things really hard.