The post-fertilisation mechanism in a human-animal hybrid works until the blastocyst stage, after which the chromosome pairing errors begin to kill the hybrid. If this can be circumvented by genetic engineering, then the hybrid will indeed survive. But the point is, the hybrid survives until the blastocyst stage, which is long after fertilisation.
So? I don’t see the connection between that and having a soul. It’s a moot point. If we can take a dead body and reanimate it in some way, does it have a soul? Is it the same person it was before? None of this matters of course, because we can’t do it.