User blog comment:LexFacie/Thoughts about Bankais./@comment-25065646-20140710180124/@comment-25162509-20140714004642

In Bleach 510, Yhwach asked Yamamoto: "What should I do? Use your bankai's power to awaken the corpses of your men, Genryuusai?"

We can assume that Yhwach was referring to those that he had slain 1000 years ago. If that's the case, then Yamamoto's bankai can summon those people he killed in general regardless if he used Zanka/Ryujin Jakka or not. Since Yhwach stole such bankai, the same goes to him; he may summon Yamamoto's corpse or any shinigami he killed thus far.