I'm curious as to how much interplay, if any, there is between the 343i art and lore departments. Does the lore team have any kind of input on the art design or do these things exist in their own bubbles? Do the artists just do their own artsy thing and the lore people must come up with the excuses and justifications after the fact?

What I've seen so far would suggest this is the case, though there are some exceptions like the Grunts' anatomy being overhauled to a more canon-friendly look in H5. But that was only after their H4 iteration received a ton of complaints. Mostly it seems the artists just have free reign to do whatever they want.