User blog comment:LexFacie/Thoughts about Bankais./@comment-25065646-20140710180124/@comment-5398287-20140713232300

Hm. Looking through Cnet's translation of chapter 509, here's what Yamamoto says about the ability:

Yamamoto: Kaka Juuman'oku-shi Daisoujin. // Gathering the ashes of all those I have slain in the past... / ...my blade imbues them with heat and forcibly awakens them. // These reawakened dead become my faithful servants... // ...and pursue whomever I deem their enemy... // ...until that enemy turns to dust!!!

If it's just people he killed in general and not specifically with his Bankai, and the same effect applies to Yhwach (since he stole the Bankai before killing Yamamoto and all that), then it might be possible for him to bring forth his skeleton to fight for him. Granted, now that he's in the Soul King Palace it might not have as much of a horrifying effect on the Royal Guard as it would on the captains, but it would still be interesting.