Yes, it is possible.
In theory it is possible to have whole level to have GI, shadows and everything in the level. If you bake whole levels textures this will result in huge amounts of unique texture infos so the level will be extremely short.
Combimining wise use of vertex lighting and baked light is the best "golden way" to have good quality and not so short levels. I would still recommend not to bake every single texture with lighting information though
**edit..
I think I could actually make a small test room of it