Again, I have done it and yes oil from the VVT o-ring that goes on the camshaft can make its way out. All doesn't stay inside the engine and it definitely can leak out via the cam seal. You are forgetting that sometimes things are not an all or nothing. Like, a hand-drawn pic of a part does not factor age/wear related issues, such as hardness, slight rubber wear, heat cycles, expansion/contraction, etc. An o-ring doesn't have to be 100% blown or leaking 360 degrees. So, yes, the o-ring can still leak and provide some VVT movement. The way to know this is from experience with the parts in hand, not desktop studying alone. Call it surface adhesion of oil, flow, pressure, centrifugal force that whips the oil out towards the cam seals, whatever, oil from the VVT can make its way out.
Why not do the VVT (external) o-rings? You have to remove the VVT hub anyways. Then the o-ring is right there, exposed, and literally 10s to replace.
If you are thinking, why do it anyways if in 60k miles the VVT hub wears out (or internal o-rings), I don't understand. You are talking about the VVT designed in the latest iterations (so good quality) and you have been using synthetic oil. What if it lasts past 200k miles? I did both on a Volvo with over 125k miles and the VVTs were tight (fluid smooth, but tight) and the o-rings leaked, but was caught early.
I am not sure it is wise to skimp on cheaply priced rubber known engine parts that go bad when they are wide open for easy fixing when doing the camshaft seals job. O-rings definitely flatten and harden with heat and age, both for the VVT and the end plugs. Rear cam seals are ~$4 each and are exposed in order to use the alignment tool. When the timing belt is off too, a great time to get a new one if it has been soaked or exposed to oil. Not sure what the argument is of not changing the worn rubber parts when it is already exposed or removed.
From someone who has done these, trying to help so the job doesn't have to be done twice and prevent something worse.
2008 XC90 3.2 AWD - 150k miles, Premium, Versatility 7 passenger, Climate, Convenience, retrofit Morimoto D2S HID bi-xenon, iPd swaybars & poly bushing inserts, Powerflex poly control arm bushings, Bilstein Touring Fr struts, Bridgestone Dueler H/L Alenza Plus 255/55R18, Fr Infinity tweeters & speakers, hardwired cheap $17 Bluetooth to center console aux & pwr, CQuartz UK 3.0 ceramic coated, no oil consumption using Mobil 1 0W-40 even w/ my lead foot