Ok, I managed to find a way around the bug. Here's how:
First, I noticed that casting Raise Dead on Kachiko would actually set KACHIKOREBORN to 1, only no cutscene would happen.
So, before casting Raise Dead, I used CTRL-Q to add Kachiko's corpse to my party. This way the cutscene triggered correctly, but I was stuck with two Kachiko: the new CG one, with all her equipment, and a naked LN one, i.e. the body. The problem being that the corpse-Kachiko couldn't be removed from the party, since she wasn't anywhere.
The solution I found: use CTRL-Q to join the corpse in the party, then remove it from the party, and *now* Raise Dead her. Now the cutscene triggers fine, and you aren't stuck with extra Kachikos. VoilĂ !
I'd include some info about my installation so that this bug can be explored, but it's a quite complex one: Tortured Souls, Shadows over Soubar, Check the Bodies, plus 25-30 smaller mods. I'm pretty happy with it, given that this is the first serious bug I've encountered
(the other being the Potions of Mirrored Eyes doing nothing against TS basilisks)
PS: Something to fix: Yoshimo's personal Katana doesn't recognize CG Yoshimo as its owner anymore.