Morris - Explicitly, in Cold Days. Lily (Summer Lady) tells Dresden about Nemesis, and tells him of his first three cases and confirms it.
Implicitly, not explicitly.
"And ... this plague. What does it do?" I asked.
"It changes that which ought not change," she said quietly. "It destroys a father's love for his family by twisting it into maniacal ambition. ...
"Victor Sells the Shadowman," I whispered. ...
"Yes," Lily whispered. "each of them was tainted by the contagion. It destroyed them."
Let's assume Lily knows what she's talking about and hasn't been fed a line by Maeve on this count. This is a fairy talking, so we can't take what she says at face value. We have to parse it for weasel words. Kravos is one of the "them." We can use him for an example of how "tainted" and "destroyed" don't necessarily mean infected. The events of
Grave Peril were obviously orchestrated by a faction tangled up with Outside. Who's a pawn and who's moving the pawns will probably be unclear for a good long while. Kravos could have been manipulated (or down stream of someone manipulated) by Nemesis. Therefore he was tainted, but not infected, by Nemesis. It's obvious that he was destroyed by the scheme's being played out in
Grave Peril.
My opinion is that if Lily hasn't been fed a line, then it's more likely than not that Victor was infected. Without that assumption, I can't say it's more likely than not.
Why would Maeve lie? Because she can. Because the effects it has on Dresden. The shock alone affects his judgment. He now "knows" he can't necessarily trust any of his mortal friends because mortals are susceptible.
Victor Sells can be accounted for by the damaging affect of Black Magic. The FBI agents by the effects of the hexen wolf belts and so on.
Sells could have been fed black magic by a Nemesis infected agent. This would have "tainted" and "destroyed" him. Same with the wolf belts.