This is an old question that lingers on the unanswered queue. Nowadays, it would be migrated to Academia.SE, but that site didn't exist when this was asked. Anyway, I'll try to answer, in case it helps future MO visitors.
First, yes, this kind of thing does happen. It's known as a "spousal hire." I've seen it happen many times during my career. For example, as an undergraduate at a small liberal arts college, two of my professors in the math department were married and were already married before they got hired. As a PhD student, there was another couple in the exact same situation (both in the math department). I'm now a professor at a liberal arts college, that has around 200 tenure-track faculty. I know of three cases of a married couple that was already married before they got hired. I know of other cases where one was hired and then years later was able to get their spouse hired. I also know of many cases where one is hired tenure track, and the spouse is hired on a long-term, renewable, but non-tenure track line. The difference often depends on the research productivity of the spouse (if they have a PhD but don't do research, they get the latter type of appointment).
I've been on hiring committees where we've been open to trying to arrange this, though in the examples I can think of, the candidate/couple didn't take the job offer(s). Indeed, we have language about spousal hires in our faculty handbook, which is publicly available.
Spousal/Partner Faculty Appointments
As part of its program to attract and retain faculty, Denison attempts to offer continuing non-tenure-track appointments to qualified spouses/partners of faculty. Such appointments are initially contingent upon institutional need and the qualifications of the spouse/partner; reappointment is contingent upon continuing need as well as satisfactory performance as determined through the regular review process. These will normally be part-time appointments. Spouses/partners in such appointments are eligible to apply for full-time positions, including tenure-track positions, when they occur.
Bigger universities can often solve two body problems more easily than smaller ones, because they have more overall demand, bigger departments, a wider variety of departments, etc. Most liberal arts colleges don't have a statement in the faculty handbook like the one above. At a liberal arts college, the issue is that, if the spouse's natural department doesn't have need for additional professors (based on student demand), then it would be harder to create a tenure line in that department, but it's still possible if the spouse is a strong candidate in their own right. Often, it's easier for us to arrange a spousal hire when the spouse is also a mathematician; for one thing because our department always has plenty of student demand, and for another thing, we're unlikely to object to a new tenure line. But if they're trying to get hired in some other department D, you could imagine a situation where the spouse's research interests run counter to the prevailing theme of department D, and they would prefer the spouse on a non-tenure line.
Lastly, there's the question of when is the optimal moment to ask for a spousal hire. Generally speaking, the answer is "right after you get your job offer." That's your negotiating window. If the spousal hire is most important for your overall happiness and success, this is where you need to ask for it, argue for it, and fight for it. That might mean you get less start-up funds, etc. But, if you accept your offer without mentioning the spouse, and then hope they can get a job later on, things will be worse. For one thing, there will be less pressure to give you what you want. The spouse might be offered work as an adjunct, but once they've shown a willingness to work for the university under those conditions, it's unlikely that a tenure track offer would materialize. Department D may try to keep the spouse as a long-term visitor, and use their next tenure track hire to get someone else, thereby growing. From what I've seen, to put the pressure back on the university to truly solve the "two body problem," both you and your spouse might need to go back on the job market and get a competing offer. This is why it's best to get the spousal hire right away, before you've moved and put down roots. This advice is echoed in many threads over on academia.SE, that I link to below (in no particular order):
https://academia.stackexchange.com/questions/164166/when-is-it-appropriate-to-ask-for-spousal-hire
https://academia.stackexchange.com/questions/186289/what-is-the-long-term-professional-status-of-a-spousal-hire
https://academia.stackexchange.com/questions/127114/spousal-hire-for-girlfriend-in-us-university
https://academia.stackexchange.com/questions/56936/how-to-approach-the-dean-and-or-provost-about-a-years-old-two-body-problem
https://academia.stackexchange.com/questions/32369/when-during-the-application-process-should-a-candidate-mention-that-their-spouse
https://academia.stackexchange.com/questions/164166/when-is-it-appropriate-to-ask-for-spousal-hire
https://academia.stackexchange.com/questions/157752/two-body-problem-in-academia-in-the-us
