There's a difference between working together as teammates or just being based at the same location, but different departments, and having one spouse/partner in a supervisory role.
For some companies, this is an extreme no-no because it looks like nepotism.
In the past this has come up at my company, on teams I was a part of. There were people who were dating, one was an assistant manager (with whom I did not get along) and one had just been promoted to a manager position from an assistant manager on another team. When the new manager took over, the assistant manager was shifted to the other team.
It just looks bad when it's supervisor/supervisee because of the implications that the supervisee is getting "special treatment" - whether he/she is or not.
1st-time Mom to DD (3/2010)
"Make mistakes! Get messy!" - Miss Frizzle