No, Infusions are specifically neither Arcane nor Divine magic, and therefore the Artificer does not meet the "Able to cast 2nd level spells" requirement for Mystic Theurge.
I meant "levels of a spellcasting/infusion-using class" when I said spell/infusion level. Sorry for that confusion. 17th level spellcasting (i.e. 9th level spells) is great, but not getting that til 20 means you should be getting some incredible stuff in return - and while I've never played an Artificer and can't specifically comment, I do know that 13th level spellcasting of another class is not worth 3 lost levels in your primary spellcasting class; I suspect 13th level infusion-using isn't either.
Though, I could certainly see this as a better item crafter than any other, which is what it's supposed to be, of course. I'd consider knocking the spellcasting requirement to 1st level spells, though, and allow entry at 5 (Wiz 1/Art 3/Sort 1), so you can get into the class earlier, and those feats are delayed less. Because no matter what you do, Wiz 3/Art 3 is going to suck.