If this was a side effect their pool was almost certainly vasectomy candidates, and rather than there being compensation, they probably didn't need to pay for their treatment.
> One volunteer did not recover within 4 years since his last injections.
It didn't say his sperm count was actually zero.
Generally IVF is still possible when the male is classified as "infertile" by traditional measures (i.e. extremely low sperm count or dysfunctional sperm).