It would be better to put all virtually static lookup tables in their own file/filegroup and only backup that filegroup or do index maintenance when something changed.

As far as putting all lookup tables in their own lkp schema, that would make it obvious that a table was a lookup table but it's a whole lot like prefixing table names with "tbl_", which I don't care for at all. It would also separate lookup tables from their dependent tables and that can make life a real pain when you look at the tables in Object Explorer.

Personally, I'd dump the idea of using a separate schema for lookup tables.