User blog comment:B214/High School DxD EX/@comment-26527700-20150629113356/@comment-26209278-20150629152744

Children by nekomata are considered nekomata, not hybrids.

And i think it's basically what you said. For example Rias and Issei, the child would be a halfblood (but still full) devil. Not pureblood, but not a reincarnated one. And not a devil/human hybrid, if you get what i mean.