I suppose that might be an interesting experiment, if you wanted to better understand the ontogenetic color change that black milks go through. Would an f1 hybrid turn black? f2? Is the melanism a simple recessive/dominant trait, or is there something more complex at work, as with the "tangerine" gene in hondurans? I guess you could find out the answers to those sorts of questions. There's also a fair probability that you'll just wind up with big, ugly, heavily tipped hondos that no one will want to buy. The real results may not come until the second generation, and since black milks take 3-4 years to mature, that could be a very long-term project.
And of course, there's the question of whether to keep them at room temps like a black milk, or warmer like a hondo... that's why I suggested Andeans for the cross, since those have similar requirements to black milks, and a similar size, too. Then again, with hondos, you could start introducing hypo/anery/albino genes, that could be interesting. Anyway, with sufficient forethought and clear goals, I don't think hybridization is necessarily a bad thing... good luck and please think ahead carefully!