I'll put this where it is: One, I am not in a position to make a decision on it. I am simply not a programmer, and so cannot make any serious technical assessments on the feasibility of such a move. Nor do I have authorization from the various contributors on re-using their content.
The critical component for anyone on the ONR team, before agreeing to any such arrangement, would be commitment to historical accuracy. This whole thing, since long before I got involved, has been an experiment in realism. Any elements that would not pass as material for a doctoral dissertation are not acceptable (excluding a bit of comedy relief, like seeing how absurd-looking we could make "Sharp-Wave", and even that has to be feasible). I have not studied the Shogun mod, and do not know what exactly they are building... but to get anyone from this project to help, they would effectively have to agree to that condition. Pretty much everyone on this team is an academic historian, and most of us are at least fair swordsmen in real life.
Furthermore, we are waiting on Fujiwara because we lack a programmer. Without him we can't port this thing to 1.0x or Warband. So all the quests and setting material you mention is going to require attention. And I somehow doubt that ONR needs models for very much ... the ones already in-game are geometrically accurate, and deliberately low-poly (to go easy on the hardware). Except for a few items of interest (horses with Japanese saddles, for example), most everything is modeled.
Now, if any programmer from one of those projects wants to come over here and help, I think I have the support of the rest of the team in saying that we will take all the help we can get. I would like to see this thing back on track. But I wonder, from your description, if there is any direct benefit in the merge you mentioned. I would have to look over the situation a little more carefully.
Just looked over that mod ... at least the screenshots and the like that they have posted. Their history is all screwed up. Models are from all over the place, half of them Chinese or the like, from 12 different centuries, plus whatever they could find in fantasy films. Half the weapons look more like they should be used by orcs than samurai. Textures are, in many cases, that crude cast-iron metal look from M&B Native - not at all the polished blades of Japanese swordsmiths. The building models, too, are from all different centuries, and not at all arranged in any sort of historical design. (They have "ninja" running around on an open battlefield wearing black pajamas, like that's going to help outside in broad daylight.) The whole thing looks like a bad knock-off of some Japanese cartoons.
And to make it worse, the models are high-poly and textures are high-resolution. Only those with new computers designed for games are going to be able to run that on a battle of any size. That's going to eliminate the older crowd that has been the backbone of ONR ... professional historians, university profs, and the like, seldom have that type of hardware. What could be worse than bad designs rendered in extreme resolution, so you can really see how bad they are?
Compare that to ONR, where pretty much every piece of equipment is measured from museum pieces, of the right period and location. Before adding anything, there have been major debates on how much a particular piece of equipment was used, which surviving examples we should use for models, and who should get them ... all the way down to what kind of hats certain people should wear. I just don't think we speak the same language.
I'm going to go out on a limb, and say that I doubt anyone involved in ONR is going to want to work with those people, unless they specifically want to help here (and accept the culture and spirit in which ONR was made).