I'm not advocating any hybrid or inter/intra-specific cross. I was just correcting you in that there are TWO other species that have ALREADY been crossed with Balls, other than the ones you've mentioned.
But I wouldn't cross out the Angolans. It was most likely an Angolan male to a normal female BP (no one would waste a female Angolan breeding year at this stage of the game). But I still wouldn't do it. And not because they are ever going to be re-introduced back to the wild, because they won't.
The only thing I disagree with is hybridization between species when such hybrids are fertile. If they were infertile, I wouldn't care.
If the offspring are fertile, then by the scientific definition of a species, the two snakes in question are not different species. (devil's advocate). Makes you wonder........