I was just going by the mainline appearances and basing his absence on those, but yes he does also get a brilliant side story in Kenzan
Yeah, Akimoto was one of many cuts from Yakuza 3, for whatever reason a number of side stories were cut from the English release, many of which made no sense to omit them but I guess Akimoto got cut because of the while [spoiler[ Incest [/spoiler] thing. Still not a cool thing to do, since I thought it was done in a more comical manner and not a seriously graphic or sexual manner.
As for Shinada, I'd have loved to have him appear in 6 just as part of the Baseball mode. Seems like such a glaring omission (and 6 sure has a few of those!)