Battlefield Enchantments only work once per battle. Different Battlefield Enchantments work together. Manual lists them as BE. There are also spells that affect the whole battlefield but aren't BEs. I expect they'd be something like Rain of Stones and such, and they stack.
Yep, the ones producing a lasting effect (foul vapor, darkness) don't stack, when the so-called (by someone at least ) "instants", like master enslave and rain of stones, give one effect instantly only, so they can be cast again and again.