Wrapping the special graphics into a tileset seems preferable in that the game engine that needs to display and run the level, it wouldn't have to do special code to handle the special graphics itself, the terrain would simply be just a tile like any normal set.
Given a level using graphics set N and special graphics set M, an equivalent tileset would have the following:
- terrain: one single tile corresponding to the entire bitmap from set M
- interactive objects: same interactive objects as set N, except with a palette swap using the palette from set M's bitmap
If your database need to support exporting the level back into files formatted to be usable in the DOS game (the level DAT, vgagrN.dat and vgaspecM.dat), you may want to at least keep some information in the database to aid with the export operation, specifically the values of M and N. This would allow the export operation to detect and therefore perform special handling of the "tileset" to properly "unwrap" it so to speak, so that you can end up with the vgaspec file.
