No, lots of interspecies sex is what it is. Most cultured Zentradi don't go with the cloning thing, they found out on what they were missing out on. Even Kamjin Kravshera who despised humans took a liking to "doing culture". And many got with humans (a la Max & Millia) because humans knew what they were doing and they didn't.
The vast majority of a good generation of humans born after Space War 1 *are* clones on the other hand, but that's because the Zentradi nearly wiped out humanity. But after about 20 years the large-scale cloning was stopped. The limited genetic base left meant that even with a lot of playing around with genetics, a lot of previously rare inherited diseases were becoming exceedingly common. The human genetic base is probably destined to be absorbed into the Zentradi one in the long run.