RAW: Ambiguous

The rules are not clear on what, exactly, constitutes an “arcane spellcasting class” or a “divine spellcasting class,” probably because initially it was obvious. By default, assassins, bards, sorcerers, and wizards were the arcane spellcasting classes, blackguards, clerics, druids, and paladins were the divine spellcasting classes. There was no ambiguity: the former are the classes that cast arcane spells, and the latter are the classes that cast divine spells. Easy.

Then they printed things like Alternate Source Spell, Rainbow Servant, Sha’ir, and Southern Magician, which introduced ambiguity that hadn’t existed before. In these cases, you have spell slots from one class being used for either arcane or divine spells.

Does this new feature suddenly make the class into an “arcane spellcasting class” or “divine spellcasting class” where it wasn’t before? There hadn’t ever been a strict definition before, and they didn’t print one at this point, either. Some of these effects seem to try to include wording that prevents this kind of thing, but much of those rules are also unclear. For instance, consider this from Southern Magician: “The actual source of the spell's power doesn't change,” which Customer Service interpreted as preventing entry to mystic theurge. But it doesn’t really say that, does it? It says something about power source, which is unclear.

Unfortunately, there’s no direct, rules-as-written, “as it says on page xyz of Complete Shenanigans” kind of answer to this question.

Recommendation: Never

RAW is ambiguous, but what’s going to work well in-game is not: never, under any circumstances, should one be allowed to advance wizard spellcasting faster than the wizard does. That should never, ever happen in any game, and if you’re going to allow it you might as well allow Pun-pun.

Allowing these sorts of tricks to qualify for mystic theurge, and other prestige classes and feats that require one type of spellcasting or the other, is pretty clearly legal, RAW, and also usually far less troublesome. The only exception I’d be likely to make is the dweormerkeeper from Complete Divine’s web enhancement, but then I’d probably just ban that class outright.

Even allowing a divine-only prestige class to progress wizard spellcasting is almost-always not a problem. It’s the double-progression that should never, ever happen.

Metamagic Master and Wayang Spellhunter are the same trait…

It's unlikely that a GM will allow one creature to take both the Metamagic Master trait and the Wayang Spellhunter trait. Although both are regional traits and many GMs do ignore the rule that says that a creature can't take more than one trait from each trait category (see here on Restrictions on Trait Selection), the traits are also the same trait: The d20PFSRD renamed and changed the description of the trait Metamagic Master to remove product identity from the trait Wayang Spellhunter. There's no Metamagic Master trait in the Dragon Empires Primer as per its provenance on the d20PFSRD, only Wayang Spellhunter.

…But the benefits of Magical Lineage and Waywang Spellhunter can be combined

Except in rare case, bonuses of the same type or from the same source don't stack, and, instead, only the highest bonus of the same type is applied. For example, the trait Elven Reflexes and the trait Reactionary each grant a +2 trait bonus (the bonus's type) on initiative checks so a creature with both traits gains only a +2 trait bonus on initiative checks.

However, the benefits of the traits Magical Lineage and Waywang Spellhunter are not bonuses—and even different benefits—, so the two traits can work in conjunction.

This means that the benefit of the trait Magical Lineage can be combined with the benefit of the trait Wayang Spellhunter (i.e. Metamagic Master) to allow the creature to prepare in (or cast using) a 2nd-level slot an intensified empowered shocking grasp spell.