Yeah, but its one of the few jutsus that require external materials(ashes/pieces of the person being summoned, a live[maybe willing] sacrifice, and your own blood). And seeing the ninja process of dealing with dead bodies makes the first one ridiculously hard to get depending on when the person dies. Kabuto, being a medical nin, should know how dead bodies are dealt with and thus know the most plausible ways of obtaining materials.
Originally Posted by Kyuubi clone
Concerning your last two sentences, that was already mentioned. Since Kisame and Samehade fuse/share chakra, their chakras were assumed to be similar by the medical and sensor nin.
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