A CL 5 animate dead scroll can animate 20 HD skeletons and zombies (the max, if you're not animating dragons with the Draconomicon rules) if you cast Desecrate first. So all you need are a few CL 5 scrolls, or one CL 5 wand of Animate Dead, and a way to cast Desecrate (another wand, etc). The variable material components is a problem, but even if you just pay enough to animate 20 HD for each charge/scroll, it's still a LOT cheaper than making constructs.
The so-called "higher" forms of undead actually usually suck compared to just using a bunch of skeletons and zombies that you've put even weak equipment on. They're a pain in the ass to control, usually have some kind of vulnerabilities, and you also have to worry about them turning on you if they break free of your control somehow. You also usually can't control very many of them... at least safely (I don't consider a chain of spawned undead controlled indirectly via controlling their creator to be safe at all...). Meanwhile, the guy with the skeleton and zombie army can have a huge amount of physically powerful minions for a lot less work, and less danger to himself.
And even if the artificer's CL 5 animate dead wand uses up more onyx than he needs (assuming he makes it so that each charge can animate 20 HD), he'll still be able to craft his minions' equipment more cheaply than a "real" caster would. So he'll probably break even.
So yeah, I think an artificer could make a decent necromancer. The only way he'll be behind the other casters is in the application of feats and class abilities that buff his minions up as he creates them (Corpsecrafter, etc). But then again, he's still an artificer... He hasn't actually dedicated any feats or class abilities to this at all so far. Just a bit of his WBL... So literally any artificer could add this undead horde on top of whatever else he's doing.