If you code an engine (in asm), it's not counted during the jam.
The only thing that is "counted" is the game during the game jam , before that you can code an engine, a library etc
And it's highly recommended because it's nearly impossible to make a full asm game from scratch for the SNES.
This is why the gamejam is announced well in advance to let people prepare in terms of code and assets (because yes open game art or other is accepted for assets).