There is two kinds of rules here that you seem to mix up.
- Don't have a relationship that could make you appear to be influenced in important decisions by it or that could make it appear as if you used your professional authority to coerce someone into that relationship.
- Be extra careful in general when trying to establish a private relationship with a coworker, the more private the more careful/slow to establish it you should take it and the more it could be a case of 1) the more you need to think about resolving the underlying issue that makes it a case of 1), i.e. you may need to switch departments if you otherwise are your spouses manager as his/her colleagues could see favouritism in your decisions, especially if you run a competitive team.
Probably both rules could be formulated a bit better to be perfect fits but I hope you can grasp the general intention. Rule 1 has been discussed in a few answers and should be pretty straight forward: Your company will not like it when you make them look "corrupt" to outside clients (e.g. if your spouse represents a client you do major deals with choosing their company over competitors) or when you poison the company culture because your team members think you favour your dating partner. Neither will they like the prospect of you opening them up to being sued for sexual discrimination etc. Obviously this is also potentially a career killer.
Rule 2 exists because you cannot walk away at the work place from a dating disaster. If you approach someone and that is unwarranted, clumsy or might even come across as creepy - even if accidental, in a bar you can walk away, never to be seen again and both of you will forget about it. In the work place that can easily mean your relationship with that colleague is poisoned. Have a few such cases or an overly irritated coworker and you might quickly be known as the guy or gal that wants to get into everyone's pants. Not a good career move either. And the other way around, even if it does not come back to you - many people consider work just work and they don't want to be annoyed by dating approaches in that environment, but they want to feel valued for their work, not be wooed for their looks and charisma. So it's also a question of respecting personal boundaries and in particular the boundary between private life and work life.
If you take it slowly, nothing speaks against dating someone from work. In fact, work is a perfect place to find someone suitable, as you can observe people under every day situations, how they react to stress and how the are at their worst rather than their polished best. It's also actually a good place to get to know the person and not the idolized sex object - if you properly take your time.
The work place (along with school/college) typically is one of the more common ways to meet a partner. While the number vary between different surveys,see for example this one:
And from personal experience, couples that meet at work typically also are more stable than couples that meet, say, on Tinder. Likely because the barrier to actually start dating (and make that visible) is also higher and people therefore take more time to decide whether they should make a move.
All that being said: Rule 1 would not apply. Rule 2 would to a slightly lessened degree. Feel free to make a move at some point, but be careful about it, i.e. just start to get to know that person rather than outright ask her for a date.