The name "wiper" came from blending "white bass" and "striper" to fit this hybrid striper. Since there are multiple thousands of known fish hybrids, calling any one fish a "hybrid" isn't very descriptive except among anglers who talk only about hybrid stripers. In the same fishery might be found some hybrid bluegills, crappie, and maybe a hybrid black bass.
Wipers are not sterile, can occur naturally.
Reference: CRAWFORD, T. M., M. FREEZE, R. FOURT, S. HENDERSON, G. O’BRYAN, AND D. PHILLIPP. 1987. Suspected natural hybridization of striped bass and white bass in two Arkansas reservoirs. Proceedings of the Annual Conference Southeastern Association of Fish and Wildlife Agencies 38:455-469.
They simply are not represented in high enough numbers in any fishery to effect a significant hatch, and most can't go far enough upstream give an egg a chance of hatching. They run upstream with either white bass (to home spawning areas) or stripers and can contribute to egg production and fertilization. The reason is striper eggs are not attached to anything, left to suspend in current, fertilized in a cloud of milt. Fertilization is very random among three fish species. Like the striper egg, the wiper egg must also tumble downstream 2-3 days before hatching. Both wiper and striper are not likely to reproduce in a reservoir because of the water flow requirement, so stocking them is required to maintain a significant population. A hatchery collects white bass eggs and striper sperm to produce fry to supply fingerlings.
The third fish in the mix, the white bass, produces eggs that attach to hard surfaces, but they like wipers and stripers don't guard the eggs like black bass and crappie (guardians), and they like to spawn in moving or turbulent water, unlike a largemouth bass. The white bass has a high tolerance for hot and cold water, while the Atlantic Striper has low tolerance for extremes, so the wiper provides a powerful creature with the better attributes of the parent fish.