Yes I have grafted weeping mulberry. The scion of normal mulberry grows straight up on weeping mulberry. It is in all cases I have seen the mulberry scion that does the weeping growth and not the rootstock. There have been friends who had the scion die and rootstock grew straight up. All that said if someone made a cutting of the scion portion of weeping mulberry to use as rootstock it’s possible it could influence weeping though I have never seen that. A word of caution in my environment the scion part of weeping mulberry is not overly hardy and dies leaving the hardy rootstock. If your grafting to a less hardy tree your scion that portion also dies. You are correct male mulberry can be grafted to female. After having said the rootstock does not influence the weeping in mulberries in my experience it does not mean that is necessarily always going to be true. Every weeping mulberry I have encountered seem to be made from scions from the same type of weeping mulberry. So you might ask why bring it up ? The answer is sometimes the rootstock has great influence over many things but its not typical. Just because that’s my experience does not mean someone has not developed a better weeping mulberry. Here is an example of rootstock influence on scion