Just woke up so hang with me here..
Nothing in my experience bas ever lead me to believe datnoid cannibalize. Obviously we're talking living animals here so it's not something to just do willy nilly but I can tell you I currently have datnoid pushing 2" with my 4" NTT and 10 or 11" IT and the bigs have never gone after or tried to eat the little guys even when they were added to the tank at closer to 1" in size. This is in a 180 tile bottom tank with limited hiding spots and all of the fish spend a good amount of time in the wide open and around eachother.
Years ago, maybe 7 or 8, I had a similar setup to this as well only it was a 75g. I had two probably 13" IT and added them to a tank with a few IT measuring around 2" and they never gave them a second glance.
Every time I've personally had very small datnoid with larger individuals the little ones flare up to "110%" stability if you will, lol. It seems to be something of a, "Hey! We're on the same team, I'm one of you! These spines on my back won't feel great going down your throat!" It seems like they're identifying themselves as another datnoid and the bigger ones seem to know and leave them be.
I don't use live feeders for any of my fish but it in an older set up where the scenario was similar to yours I had a South American "Gar" (type of super tetra basically lol) who I was using feeder guppies to train onto pellets. Idea was to get him knowing when it was coming and hit the surface to beat the datnoids to it and over time I added hikari sinking pellets more often until he realized he liked em then he ate anything. Well needless to say a few feeder guppies hot past it and the datnoids happily ate them but never once that I saw even looked at the little 1-2" dats as a snack.
If you decide to try this take precaution, maybe a critter keeper to create a barrier at first and not a bad idea to feed them well maybe an hour before introducing the little one so they don't have any additional temptation.
I know I'm not the only one who believes this seems (key word seems) to never happen so others may be able to give you their $.02 as well and you can decide what you want to do from there.
