Requirements for ability to reproduce
The ability to produce offspring has more to do with the compatibility of the chromosomes than the number. This is why hybrid species (such as mules) are able to survive (but are infertile). If you want to learn about why hybrids are infertile here is stackexchange question about. 

Although, this would all be dependent on weather gametogenesis could occur with the tetrasomy. But as seen here with Down syndrome, it can be successful.