SEED_IT is not a dll - it's more a tool that generates c-script/lite-c (extendable) you include with just one line in your existing or new project.
You draw a seedmap and define with SEED_IT how the models should be placed (automatic) in your level. And you can change many, many options of the placement with just a few mouse clicks whenever you like.
To your question: yes - with SEED_IT you can create an unlimited* number of seedings per level and you can seed on multiple terrains by just one seedmap (scale) or by many (scale&|shift).
Take a look at the SEED_IT online help to get an idea what SEED_IT can do for you.
