Vesper I think knows his players are new, he outright said he's made something to the effect of "A game that is easy, but feels hard." when he was talking about new players so I think he knows completely that Magni is going to be a little bit of a glue eating idiot with his first real attempt at DnD. Let's be real, Vesper is an incredible nice guy for the most part especially to his fellows, I doubt he'll make a meat grinder dungeon at level 2 (the level he says Tempus will start on-stream, as they'll be playing level 1 off-stream as a test) just to really test his players. I'd expect something like that to show up around level 5 or 6 if he knows about the power spikes innate to 5e's system where level 5 is an entirely different game due to how extra attack and 3rd level magic changes the game. My only doubts with Vesper is he is a Pathfinder 1.0 kind of guy from what he said, so I don't know how much he actually knows about current age 5e as far as running it.
I personally think Altare may have his own kind of issues, as Altare has shown to have some genuine insecurity issues with his streaming. I wonder if he'll try to do something cool to be part of big moment and just fall flat on his face due to bad dice rolls or just overextending into a situation that he didn't understand, and then he just feel deflated over it overtime as he fails. Altare does this with his gaming streams where he malds and tilts because he feels he is doing poorly live on stream, blue boy just refuses to be bad at video games and has admitted that he wants to be the "pro gamer" of Tempus because he feels he offers nothing else compared to the other three. So I wonder if that will happen in something like DnD given the "Critical Role" effect that is just part of DnD's normie sphere these days where people try to LARP like Critical Role actors, fail, and just quit DnD entirely. Plus it is doubtful Altare had a DM as potentially harsh as Vesper, so who knows how he might react to Vesper's more older school style.
I personally would try to push for a TTRPG "Elysium" theme setting if I were in his position, because I think vtuber lore is just underexplored in Holo in general and this feels like the perfect chance to do something with it that can be fun and maybe even remotely interesting. The only real issue imo is Vesper NPCing anyone Tempus member that isn't himself, because that can be weird to DM in the moment and you don't want to create a weird plot hole that effective asks "Why doesn't Guild Tempus just do something about the dragon coming to threaten Elysium?". I'd personally do the legwork with management to make it happen if I was allowed to do it, but maybe management just said no outright and that's just the end of it.
I just to see a situation where they go to "Northern Elysium" where everyone talks like Axel so Vesper has to do an Axel impression, and we learn the "Syrios" family is some kind of rich off their ass noble family where Axel is some kind of wayward son who just fucked off to become a singing Gladiator for Tempus. This would mean that what Altare said about getting 10 million USD to start Tempus to wingman for Axel trying to impress Nodoka was an actually true thing that really happened within Tempus canon.