Though each of these two stories is substantial enough to merit its own review, they share enough similarities that I should comment on them together. Both stories take place in a world where Lovecraft was a sort of reclusive Truman Capote, writing non-fiction using the tools of fiction. Both stories also attempt an inversion of the good/evil spectrum present in the original Lovecraft stories to which they refer.
To expand a bit on the first point, "Live Bait" features a businessman making a visit to the town at the center of "The Shadow Over Innsmouth," a story based largely on the nameless narrator's first hand narration to HPL. "The Black Brat of Dunwich" is the story of two researchers who meet someone with a rather different account of the events that took place in "The Dunwich Horror," which was based on a combination of newspaper coverage and HPL's interviews with Henry Armitage.
[I've always found Lovecraftian stories featuring Lovecraft as non-fiction author to be something of a cheat, though "Black Brat" manages to use this tired concept in an interesting way.]
And just to cut to the chase, since it will become obvious soon enough, of the two stories "Black Brat" was certainly the strongest. "Live Bait" starts strong and has moments of suspense and a few good ideas, but its attempt to cast the Deep Ones as victims fails to "humanize" them to the extent that the author may have intended. (It doesn't help that Lovecraft's original story ends with the human/monster dichotomy already shredded. Had "Shadow" ended right after the narrator's escape, the inversion would seem much fresher.) The Innsmouth locals are little better than caricatures, more like copies of Deliverance hillbillies than truly sinister individuals. (Though Sargent does a fairly good job of copying Lovecraft's odd Innsmouth dialect.)
By way of contrast, "Black Brat" is a pretty successful "humanization" of Wilbur Whateley. It falters a bit at the end; Sargent seems to be straining to wrap everything up a little too neatly. By contrast, the middle section dealing with Wilbur and the inconsistencies in Lovecraft's tale is fairly thought provoking. There is an interesting tone of homoeroticism brought to the material which surprised me on my first reading, but on a second reading it seemed very appropriate, resonating with Lovecraft's theme of alienation and body horror. Sargent handles the theme well, pushing it enough to get you thinking without letting it become heavy-handed.