No, they wouldn't. Vanilla Minecraft objects, creatures, and items are much easier to find, but the characters can bring things from their universe into this one. But, these items are more rare, since no one will be leaving New Haven during the roleplay. 

So, it's a good idea to have your characters bring renewable resources, like animals, seeds, rechargeable machines/batteries, etc. But remember, they have to be reasonable. Nobodies bringing a Doomsday Device with them.