Chimera

No, they are mythical creatures.

There's a genetics thing referred to as a chimera where a person's DNA doesn't match up to them like it should, often the result of something like twins fusing in the womb, but the mythological chimera doesn't exist.

I think, there are many spiritual beings and Chimera could be one of them.
I tried before years summonig Greece Sphinx, - in Greece mythology a sister of Chimera - and by my opinion is real. So, I think Chimera could be real spiritual beings too.

No. They are beings of myth.

Such a creature is relatively easily to Summon. But it could be more dangerous than summon a demon.

There's a god named Tutu (Kemet) who happens to be similar to a Chimera. He is often represented in the form of a sphinx with a snake for a tail, though he also appears with snakes/scorpions for paws amongst other things.

He essentially is a deity who ended up functioning as both the royal/kingly ka and the Nisut-bity (king/pharaoh) during the take over by Greece and Rome. Apparently at an earlier date there was a similar creature that represented the kingly ka, so as no one did the actions necessary to keep the universe going, he came forward as a sort of a savior.

~

On another note, I'm sure there are thoughtforms, servitors, and various beings running around that might look like a Chimera or could look like a Chimera if they wanted. After all, they aren't bound by the physical world like we are.

Chimera
http://img2.wikia.nocookie.net/__cb20120615060217/dragonsdogma/images/0/06/Chimera01.png

Marduk
http://en.wikipedia.org/wiki/Marduk#mediaviewer/File:Elam_r_%2830%29.JPG

His anorher name is Tutu (Kemet)
http://www.mythologydictionary.com/marduk-mythology.html

They probably could exist in the astral realm

No Chimeras are not real, I mean there are many spiritual animals and forms on the astral plane that no long live on earth. But anything mythical or fantasy is not real. They are on myth for a reason.

whether an astral being really exist or no can be known only through evocations - summoning. Philosophical considerations are nothing.