I can't offer a consensus on your question about the parentage of Roxy's
child, but I can offer you my opinion, FWIW. I agree that the logical
father of the baby is Driscoll rather than Essex, and that Mark Twain was
blurring the lines to avoid added controversy about miscegenation. My
"evidence": the two babies are born on the same day, one to Driscoll's
wife, one to Roxy. They look identical--and having the same father would
make that more plausible. Did Driscoll couple with both his wife and Roxy on
the same day? That would be a sickening possibility. Metaphorically, Tom
and Chambers are the "extraordinary twins," separated by Twain by blurring
the fatherhood question.
On a somewhat related note, and my favorite footnote in my book __Mark Twain
and Metaphor__ (shameless plug: Missouri, 2007), is Roxy's racial heritage.
If she is one-sixteenth black, that would mean she is the product of a long
line of miscegenation, all presumably resulting from her fully black
great-great grandmother's coupling with a white male, with each generation's
subsequent child female, and each later coupled with a white male (I am
assuming that black male/white female relations were extremely rare).
Tracing her lineage shows a nightmare of miscegenation that Twain muted but
laid before us if we think back (fictionally surmising). Five generations
of racial rape...no wonder he had to mute things.