First off, no, I don't have the slightest clue about how it is in the comics, but feel free to enlighten me.
Secondly, I'm bringing this up not because I'm a fan or I want it to happen, I'm just genuinely wondering.
So yeah, is there a specific reason the show iZombie couldn't be in the same universe as Arrow and the Flash? Before you go bite my head off, I'm not even a fan of zombies, I think they are creepy as eff, and I think those 3 shows are perfectly fine of being in 2 separate universes, they don't have to be in the same world, I'm just wondering if there's a legit reason that they couldn't be. Is there a reason like iZombie is set in a timeline of year 2008 (when the Flash hasn't become the Flash), or year 3000 (when the Flash probably won't be the same Flash unless he time-traveled)? I mean, time frame is the only reason I can think of, even if iZombie is set in Oregon (not really show if this is what the show is going for), people do travel, so I don't see why they couldn't all be in the same world, just in different parts of it.
Back in an episode (sorry, I don't have it burned in my brain), Barry told Iris zombies do exist in the world (though I think he was talking about some fungi), and from the synopsis of iZombie... it looks like it'd be a crime-solving show with, well, brain-eating elements; it'll be kinda cool if Barry shows up and lend some knowledge of forensic analysis.
Well, yeah, cuz I'm bored so I'm throwing the idea out here. I'm perfectly fine if a crossover never happens, just striking a conversation.