They shouldn't have but a whole bunch of edo's already summoned their summons(hanzo,itachi,nagato,trollkage, hiruzen)...so it's been retconned long ago.
This question was asked by me about a years ago, so let me tell you that the blood which we are viewing there is not from edo's body but of those on which they are resurrected, get that
This question was asked by me about a years ago, so let me tell you that the blood which we are viewing there is not from edo's body but of those on which they are resurrected, get that