Terence Blake has more on Harman on Caputo. He asks: does Caputo out-Latour Harman? The answer? Yes and no.
I'd turn it around a bit and go further. Harman more or less attempts to out-Latour Latour himself - see the Prince and the Wolf, for example. When Latour expresses bafflement at Harman's iteration of his ideas Harman is entirely unperturbed. In that sense isn't Harman's Latour - let's call that Hartour - a very Modern (or perhaps postmodern, small difference) version of those ideas? The objections of the author qua informant (or author qua authority in the postmodern version) are largely without consequence. Objections are not the kind of 'objects' that object oriented philosophy is sensitive to (c.f. Latour and his debt to Garfinkel and ethnomethodology).
I'd have no problem whatsoever with Hartour if Harman just admitted that it's his own particular translation/deformation of Latour's work and that it serves as a foil to the development of his own philosophy - which is what the Prince of Networks is all about, the first half sets up Hartour as both a stepping stone and a straw man (a stepping man? a straw stone?) to be ascended and then overturned. In and of itself there's nothing wrong with that whatsoever. But Prince of Networks is written and promoted like its an authentic account of the corpus itself, like a quasi-textbook, which is shameless.
On the subject of Caputo, I think that he is certainly right that Latour is not as different from Derrida as he'd like to think ("anxiety of influence", yes; I'd also say 'Oedipal reflex', something that most philosophers are guilty of!), however as philosophical predecessors go I honestly don't think Derrida would crack the top ten (Latour's a well read chap and a bricoleur of the highest quality). To suggest that Latour's philosophy is basically just Derrida in different words is pretty much BS. In fact isn't it intrinsic to Latour's philosophy from the very beginning that nothing is contained in anything else in potentia? From irreductions (as I recall it): 'Nothing is, by itself reducible or irreducible to anything else. To say something is to say it in other words, that is to translate.' Even if Caputo was right Latour still needed to do that work of translation. It can't have been done for him, not in Latour's own terms, anyway.
Of course, Caputo is the proverbial man with a hammer: to him everything looks like a Derrida! Perhaps the really unacknowledgeable trauma for Caputo is that Derrida wasn't a supremely original ubermenschen either. Their ideas are similar in some ways but that may have less to do with Latour's massive debt to Derrida than the fact that they both read Nietzsche.