I think the situation with a 3D printing service is a bit of a grey area.  Technically they do have a license of sort since their access is subject to their contract to provide a service, they are not reselling or redistributing the obj file, nor do they keep it beyond what is required to produce the model.  Basically, its like saying "Okay, I bought this model and I have a right to make art with it, but instead of rendering it myself I'm gonna upload it to my friend Bob's super awesome graphics computer to do the render, then the obj files after the render is done."  On the basis of copyright law alone I don't think anyone could make a case against that.  So while I'm not a lawyer, I would make an educated guess that there is a legal precendent for it, if not it would likely be up to a judge.

However, if DAZ's EULA specifically states (and I haven't read it for myself lately, so this is an example for sake of discussion) that you can't provide it to a 3D printer or only to one they approve or that the 3D printer must first buy a copy of DAZ V4 or what have you, then those clauses would be binding and you'd be obligated to follow it, period.  Doesn't matter if copyright law itself would allow it, if the EULA says you can't then you can't.

Like I said, copyright is one thing, EULA's are a separate issue.  You can be fine on the actual copyright and still run into trouble with the EULA.  Pays to read it carefully before you use the stuff (and its one reason I'm getting leary fo using anything by DAZ because last I looked their EULA was getting longer and longer and frankly, who needs the hassle?)

So far as the marketablility might be, you might be surprised.  15 years ago I briefly dealt with a company that was then taking 3D models made by artist and turning them into bronze cast statuettes that sold from $200 to over $5,000 each.  I also know that some in the RPG metal/plastic miniature industry have experimented with using 3D models and printers to create master copies that injection molds are then made from.  But again, you're better off buying base models that have fewer "strings" attached.