I think that you will have better luck getting your answers by posting the question at the yahoo.groups for peonies forum. Peony hybridizers often frequent the peonies forum on yahoo.

Thank you very much for the tip! :)

The Peony Database lists every Itoh I've ever looked up as infertile both seed and pollen. Southern Peony blog site has an interesting experiment back in 2013 about using a single stem with just a bit of root, sometimes none, to get new plants. Might want to take a look at that, too.Southern Peony Blogsite Peony Database is http://www.paeo.de/navigation/hilf_en_1oben.html and go to column Peony Database.

This is awesome, thank you!

The answer is Yes, even the possibilty is low.

People already did that. There are hybirds between Itoh and herbacous peonies and blooms, owning characteristics from both sides. Also viable seeds from ”Bertzalla” are reported from time to time. You can check ”planet peony” group on Facebook.