I am curious about this from the solve the mystery angle:
It is posable that if the infertility is hormone based it could result in low sex drive as low levels of certain hormones in humans can affect our sex drive, so why not birds too? What if he is incompletely formed boy? Does he crow? I read someplace on the forum someone knew someone who was trying to breed quieter roos and with the lack of crowing he noted his fertility rates dropped significantly. Crowing is a behavior the roos do that could be tied to sex drive? It seems less dominate young roos often will not crow until the dominate roo is removed... so I am wondering either biological or behavior wise what is the issue. Short of sperm counting him and having the sperm examined I am unsure (I have no idea if any one does that for roos). It could be too he has sperm but it is not good, flawed to the point no viable fertilization occurs. It will be interesting to see if the hens cross breed now that you moved them.
He does crow a bit but not as much as my other bantam. Now you have me curious, hormones, counts, behavior and so on. Mainly I'm hoping they can live as real chickens for a while, instead of like a pet parrot. I'll post picks if I get any chicks out of them. Daryl the splash bantam is already courting the smaller female and totally ignoring the serama roo. So it looks like they are getting along with the bigger bantams.
This is Daryl so any mixes should look Ok.