...actually, no, you have that about half right. Kenpachi tends to utterly ignore honorifics most the time, but he DOES use names. "Kurotsuchi", "Ichimaru", etc. Most of the time he'll just address someone as "you", but when he needs to specify a name, he seems to just use surnames with no honorifics for most the captains. He calls Ichigo just "Ichigo", refers to Yamamoto as "the old man" (haven't seen him ever directly address him), and I don't recall offhand what he calls people in his division, but given the pattern thus far probably calls Ikkaku and Yumichika by given name.

There's a certain degree of fanon that Kenpachi calls Unohana "woman", but I'm not certain where this originated from, and I'm only up to volume 13 in rereading the entire manga so I'm not certain on quotes and scenes that take place after that. It's noteworthy though that Yachiru refers to Unohana as "Unohana-san", so if she remembers the name *and* uses an honorific...

But for the most part, Kenpachi just calls people "hey, you!" or is pretty informal with names, but he DOES know the names at least of people who're significant and such. It's Yachiru that can't remember peoples' names, Kenpachi there's no indication in canon that he has any significant difficulty with it, just that he doesn't bother when something like "temee" or "aitsu" will suffice.