it depends.
the most extreme case in Dynastes beetles was between D. hercules and D. neptunus.
see the link below:
http://insectforum.no-ip.org/gods/cgi-bin/topic.cgi?forum=2&topic=20521
the same progeny successfully produced F2 and F3. That is, the hybrid offspring are viable and also fertile. However, the viability did decrease, where many larvae died soon after hatching. If you are friend with the breeder in Facebook, you can find the image of the F1, F2, and F3 adults from the link:
I am breeding D. maya x D. grantii in my lab. the idea is to create F1 and F2 offspring and use them for associate mapping to figure out the genes associated with different body coloration. So far the egg production is nice, but will need more time to find out if they hatch and the percentage of larvae that can reach adulthood.