That's it in a nutshell. The overwhelming power of Zaraki's zanpakuto puts it in the form of the initial release. Him not knowing its name is irrelevant. The overwhelming spiritual power of Zaraki allows him to bypass the need to know its name in order to get his zanpakuto in the shikai form. But because he doesn't know how to call upon his sword's name, he can't use whatever abilities it may have.
He's in shikai. That's a fact. Yoruichi says quite specifically he's the only captain who hasn't attained BANKAI. All the captains of the Gotei 13 have achieved the shikai. That's the truth. But he can't utilize the shikai of his zanpakuto completely because he doesn't know its name and thus, its abilities (if it has any).
Well, who knows. Maybe he has learned it. The name. Or maybe he has some other way of powering himself up
He does have something up his sleeve though. That fight isn't over yet.
Oh, please, Zaraki MUST, MUST and MUST use somehting different in this fight, for the god's sake, like a new power up or something like that ,his zanpakutou in released state, wherever, otherwise this thread will have about 2000 pages in this forum, mainly because if Zaraki just keeping with his boring hack and slash game, we still be engulfed in a sea of doubts...
His sword is in shikai but he does not know it's name. This is like Ichigo when he was first return his powers. His sword was in shikai but he didn't know the name until he asked.