Yes, 'increase' is being used as a verb. If there are more enrollments over time, then enrollments are increasing, and someone observing this would "see enrollments increase".
If you added a 'that', like so:
...while the ACA continues to see that enrollments increase, there are a lot...
It makes it sound like the ACA is causing enrollments to increase. Right now, I am seeing that this question is answered. Someone observing me answer the question would be seeing this question answered.
To convert to this other structure, you are correct that you would remove the 's' from the end of enrollment. But that's not all. With just that change, we have:
...while the ACA continues to see enrollment increase, there are a lot...
In this sentence, "enrollment" represents the total number of students enrolled, rather than "enrollments" representing individual instances of people enrolling. So, "increase" is still a verb describing what that number is doing.
To make the full switch, you would also need to add an 's' to the end of 'increase':
...while the ACA continues to see enrollment increases, there are a lot...
Now the ACA is is seeing "increases", and the type of increases they are seeing are "enrollment increases".
Other possible phrasings include:
...while the ACA continues to see an increase in enrollment, there are a lot...
...while the ACA continues to see that enrollment is increasing, there are a lot...
...while the ACA continues to see increased enrollment, there are a lot...
Actually, nouns that are treated as characteristics or properties can oftentimes take on the secondary role of events. Namely, they can denote the event of someone or something attaining said characteristic or property. I think by looking directly at the examples, we can better understand how the word "occur" is used in context.
The aircraft damage occurred even though about half the helicopters were moved inside hangars and the rest tied down as the storm approached, the Army said.
The way I see this, it's not the word "occurred" that's lending itself a different meaning, but rather, it's the word "damage" that's taking on an extra role. In this instance, "damage" is being treated as an event that happened, rather than a condition or state that something had. Damage essentially means, "an event where something gets damaged" here.
Brown's illness occurred as he was anticipating an unflattering article about himself in Sports Illustrated magazine, and while he does not directly connect the two events he puts ''media pressure'' at the top of his list when itemizing sources of stress.
Once again, the word "illness" is being used to represent the event of becoming ill, rather than the state of being ill.
Best Answer
It's short for "as risky a business" [as it is now]. The comparason is not vs. "business" or some other business, but vs. some other time.