This answer is valid for EASA jurisdiction.
If someone with no night vision were in the cockpit of a nocturnal flight, that person's situation would resemble Instrument Flight Rules. Am I correct?
Only to some minor extent, because at night VMC, you still see a lot around you. Surface lights, quite often horizon line, sometimes backlit layer of clouds above you etc. You have some kind of perspective around you, limited, comparing to day VMC, but much less disorienting than IMC. This is why night rating requires 5 hours of practice and some theory (8 hrs, IIRC) whilst instrument rating (IR) minimum is 45 hours, plus about 4 months of theory (talking about PPL ratings now).
In EASA member states at least, night rating and instrument rating are not dependent on each other. You can acquire night rating only or IR only. Or both.
In theory, can someone lacking night vision operate an aircraft with no more danger than a pilot on IFR?
There is no «night vision» at least in EASA terminology. If you are referring to VCL mark (limitation to fly during daytime hours only + civil twilight) in your medical, then you are probably not color safe (like I am). Color blindness, mild or severe, as far as I know, is the most frequent reason for getting VCL mark.
EASA officials state that in dark environments, color vision is essential, especially recognition of pale colors. In US, for example, pilots that fail Ishihara, Anomaloscopy and CAD tests can still be granted a SODA (Statement of Demonstrated Ability) if they show their color recognition in practice. In Australia, color blind people can fly almost without any restrictions.
So the question is somewhat irrelevant, because a person with VCL mark («lacking night vision», as you say) can be IR rated and can fly IFR during daytime, officially and safely.
Can someone lacking night vision get a pilot's licence?
Absolutely, I am not color safe and have PPL pilot license, acquiring IR now to become fully instrumental.
However, with VCL mark, you will not be able to fly as a professional pilot (CPL or ATPL) at least in EASA jurisdiction, because VCL mark is only applicable to Class 2 medical. Class 1 medical has no tolerance towards conditions that result in your VCL limitation in Class 2 medical. Not being «color safe», you won't get Class 1 medical, which is required for CPL/ATPL.
And to complete the story, some countries require only regular driver's license medical certificate to issue ultralight class B (airplanes lighter that 472.5kg, like beautiful Evektor Eurostar, for example) license. But ultralights fly in Day VMC only, so the whole night vision discussion is irrelevant in context of ULAs.