We are thinking too much on objective reality, but we can't forget that chimeras are DREAMS... In a sense, they don't really "exist" in a material sense, except as ephemeral constructs of the thought... Even if someone can Interact with them in a "physical" way when visiting the Dreaming, they are not physical, just things made of Glamour... And Glamour isn't really "a thing" - isn't matter, isn't energy... It's just ephemeral ressonance... So, chimeras don't really exist at their own, as independent beings, rather being constructs born from the minds, thus they are dependent in a metaphysical level on the minds of the dreamers... And, since they are glamour manifestations of thoughts, and since the plasmic beings of the Underworld are ALSO manifeststions of thoughts in the form of plasm, why can't one really powerful "thought" ressonate in both realities?
Note, I never said that chimera can appear in the Underworld after chimerical death like a sort of "glamour wraith" in a literal simplistic way. But we must consider that the Dream and the Underworld (or all Umbra) doesn't exist as separete entities by themselves, no more than the material world can exist without the spirit realms.
Lets imagine an hipotetical just born chimera. Lets say that this chimera spends some hundreds of years growning in the Dreaming. Over the course of time, that Chimera starts getting a lot of momentum, "infecting" the dreams of many dreamers, to the point that the "Grim Reaper" or the "Bad Wolf" gains a special place upon peoples imaginations.
Now, millions upon millions imagine and dream about the Grim Reaper.
Upon death, many wraiths think about the dreadful figure.
Wouldn't that much psychic emanations leave it's impressions on the Underworld?
That's what I mean about "leaving different images on different surfaces".
You guys are thinking about chimeras, or plasmics, or umbrals, as independent beings on their own. They are not. They exist as an interaction with the material world (and vice versa). So, a Chimera is not simply "born" into the Dreaming - it is a new thought pattern that arises into some corner of the mind of at least ONE dreamer that gives it substance.
A Chimera cannot be created if no one has ever thought about it.
Same way with plasmics.