and it does not impede tissues fusing together.
Yes it does. In water, it forms an inpenetrable barrier.
Human wounds push foreign objects outwards, and the healing starts on the inside. Ask any adult who had a belly button piercing as a teenager.
Plants do that too sometimes, or engulf them, or just not grow at all, but the healing usually starts from the outside in plants (rolling over, cambium first and then wood). Meaning any glue remains would be locked in there forever in plants.
Superglue would prevent sap exchange and the scion would be dead faster than when you would have treated it as a cutting. It's a sealant.
The reason why grafts usually fail is because there is too little sap exchange. Adding a sealant on that wound would cause some glue to seep in and prevent proper exchange. It can hinder you in doing future grafts because now there's some kind of hard plastic embedded in a branch.
Not sure if super glue is still some kind of cyanoacrylate compound dissolved in acetone, but plants (and human bodies) don't really like those chemicals and these chems can kill the tissue around the wound in plants.
So summarizing, I think it's a bad idea.