When I read your post, all I could hear was Bill Clinton during his deposition quibbling over the meaning of the word is.
For those who do not want to accept the fact that Jackson owned slaves, they could say that the quotes from Anna Jackson's books "describe hired black workers, either free workers or another owner's slaves".
But could one really believe that during the times she is writing about and in the context she uses these words... she is talking about anything other than slaves?
Well, it sounds like his man Lewis was a hireling, either free or bond. Either way, he was paying someone what Tax-Chick pointed out was a wage. That implies he didn't own the man.
I've never seen any data on what proportion of the Southern labor resource was hired labor (I mean, from an agency or an owner, or a free contractor), versus chattel slave, versus employed labor.
Granting that there wasn't much difference, back then, between employed and contract labor, as long as you were talking about free men.
In the times and the context, I think more than one interpretation is reasonable. Hiring the labor of other people's slaves was very common, and renting out slaves was a major source of income for many who bought slaves as an investment, but didn't own significant agricultural property.
On the other hand, Mrs. Jackson's being mealy-mouthed is quite "in context," as well. Ladies didn't call a spade a spade, as we do in these air-conditioned times :-).
I don't care (except as an interesting historical question, "What do we 'know,' and why do we think we know it?") whether Gen. Jackson owned slaves. Is there a moral difference between owning a slave and renting the labor of one? Not to me. Is there a moral difference between owning a slave yourself, and your wife's owning a slave? Nope. Is there a moral difference between treating a person well, and treating a person poorly, irrespective of legal status? You betcha. No one has ever suggested that Jackson treated any person, in any context, without respect for his Christian dignity, and that's why I admire him.