Nothing in the physical world (ninjutsu included) can touch Obito while he’s intangible, however ocular genjutsu isn’t physical. It’s a transmission typically based on eye sight alone, just like how Kakashi’s Kamui opens portals in the distance where he focuses his sight, so does traditional ocular genjutsu minus the portal. Add to the fact that Obito clearly sees the environment before he emerges from his dimension and it becomes apparent how susceptible he is.
I get what you’re saying about Obito being in a completely separate dimension where even if he’s able to see the outside world from inside Kamui, he can’t be reached by the chakra of someone from the outside world...much like Madara’s Limbo clones. And to address that directly I must reiterate that eye contact is all that’s needed to disturb the chakra of the victim. For genjutsu spammers like Itachi, even eye-to-eye contact is unnecessary. The only other way I could describe the above is that even Nagato was able to be placed under several genjutsus while his Pain puppets were the ones on the battlefield and not him personally.
Also genjutsu can’t be absorbed, it can only be outright blocked. I do believe that you could be right about Obito’s possible immunity to genjutsu while he’s intangible though, it just hasn’t even been remotely tested unfortunately.
"ocular genjustu isn't physical"
I guess this is where we see thing differently, from what I understood of it (and it could be wrong) ocular genjutsu sends chakra between the eyes of the sender and the victim, the sender uses it to control the victim chakra, to not be physical it should work on a different way, like maybe ipnosis, the caster could use his chakra to create an ipnotic pattern on his eye to ipnotize people who watch that for a bunch of seconds or even less
"how Kakashi’s Kamui opens portals in the distance"
This is a bit of a problem, now I think that kakashi just sends his chakra to the designated point, but if this tecnique as ever been used from one side of a barrier to another then it means it works on a different way ('cause chakra can't cross barriers, rigth?)
"clearly sees the environment before he emerges from his dimension"
You mean when he teleports? He sure sees everything when is in the intangibility state, but if he use kamui to suck himself up and then un-suck himself on anoter place he shouldn't be able to see what's going on until the eye pops out of kamui dimension
"
And to address that directly I must reiterate that eye contact is all that’s needed to disturb the chakra of the victim."
So yep same thing as before I think eye contact is needed because the chakra needs to travel fro one eye to another, but you see it as a ligth trasmitted tecnique, itachi and normal genjustu user don't need to use they eyes to send chakra, just using a finger or whatewer, as long as that chakra reaches the eye of the victim you win, to me seems clear this way, did you think the finger genjutsu works the same un-physical way as the sharingan one?
"even Nagato was able to be placed under several genjutsus"
Wasn't it sound genjustu? Also, the preta path can absorb chakra so if somehow a rinnegan user notice that a genjust is being casted he can absorb the enemy chakra, or using the deva path and shinra tensei the chakra away like he did with amaterasu
But again if genjustu for you is that non-physical thing this can't happen
"Also genjutsu can’t be absorbed, it can only be outright blocked."
If the genjustu is made of chakra then I've seen nobody without the rinnegan or the juubi absorbing jutsu, so seems like a big yes
"it just hasn’t even been remotely tested unfortunately "
yep if it was tested we would also have know for sure if genjustu are made seending chakra or not
So in the end all these question just need one concept clear, is genjutsu made from sending chakra or in an other way?
This becomes the actual question then, beacause to me seems clear that if works with chakra then all these statement on his counters are true, otherwise if genjutsu works in some other way this whole thing can be put in a bin
