If the seeds are on the threadleaf part, there will be some seedlings that are threadleaf, maybe even with red foliage. Seeds are a compilation of all the ancestors from both sides of the family AND you don't know who the second parent is.
If the seeds are on the root stock tree, there is a better chance they will look like the root stock as that tree is closer to the species tree. Both trees are Acer palmatum so, they could cross pollinate eachother.
If you decide to grow the seeds, let them mature and fall on their own (in the fall). Then they will need cold stratification to germinate.