Orochimaru said that the shiki fuujin technique is originally created by the Uzumaki clan...so,there must be some of the Uzumaki clan members have used shiki fuujin technique to seal someone or something before it's been labelled as forbidden jutsu...but,I wonder how come it's only the soul of Hashirama,Tobirama,Hiruzen,Minato and Orochimaru arms in the Death God stomach...seems like Minato and Hiruzen was the only person that use it...
That's really simple to figure out actually,
Edo-Tensai requires the dna of the one being
summon + a living sacrifice. My guess is here that
orochimaru did't do his home work well enough
to know every thing/one sealed by this techique or
he's gonna suprise us by using the last zetsu
to summon the Kuubi.
Then again you
could be right as Hiruzen said it was a jutsu
Orochimaru didn't know(highly unlikely with
him being the 2nd best jutsu researcher) and
when it was summoned he mentioned what Minato said
about the technique suggesting Minato was the