An interesting read in this regard is Jen-Pan Huang's "The great American biotic interchange and diversification history in Dynastes beetles" in the Sep 1 2016 issue of the Zoological Journal of the Linnean Society, wherein, among other strong assertions, granti and tityus are absolutely classed as separate and distinct species.
What's the point of all this?
1. The 2 million year figure for granti/tityus bifurcation may well be accurate but could also be off by an order of magnitude or more.
2. Although taxonomy has come a long way in the last few centuries, a precise understanding of species and speciation remains frustratingly elusive.
3. Ultimately, Stellar's queries re hybrid viability can only be addressed via experiment.