This mod is fantastic, I just have one issue. On my minecraft server the minecraft:overworld is a peaceful mode spawn hub while the main world is a Multiverse world which has dimension minecraft:survival. I downloaded this map from the server and dropped it in my /saves as 'bobby-fallback', but it doesn't show up on the survival world. When I load it up in singleplayer the dimension in F3 reads minecraft:overworld.

Is there any way for me to rename the fallback world dimension to minecraft:survival or a way to tell Bobby to associate minecraft:overworld -> minecraft:survival? Thanks!

I don't believe so.
What you can do instead though is to directly copy all the .mca files from the world into bobby's cache at .minecraft/.bobby/<serverName>/<seedHash>/minecraft/survival/.