The only restriction is if only one of you works here and you are married the other could not work here. It is not uncommon for two UPSers to date and get married.
This changed recently. UPS is now encouraging employees to refer family members to apply for jobs. They even set up a referral web site. It's called "Jobs for Friends and Family" and you can find links at UPSers.
Above a certain level of management, the restriction is still in place, but for everyone else as long as there is no "conflict of interest" relationships are discouraged but allowed. Thing is, UPS defines "Negative impact on the performance of an employee’s job duties" and "Negative impact on the Company’s business, or other disruption, or an unprofessional
work environment" as conflicts of interest. So, say, loud fights that get carried into work might be a disruption and grounds for reassigning one person.
The policy also says there can't be any real or
potential favoritism between people in a relationship. That could come into play even if both are hourly.
[Edited for typo]