Can I build my seeds in a schema other than my target schema?

Or: Can I split my seeds across multiple schemas?

Yes! Use the schema configuration in your dbt_project.yml file.

dbt_project.yml
name: jaffle_shop
...
seeds:
jaffle_shop:
schema: mappings # all seeds in this project will use the mapping schema by default
marketing:
schema: marketing # seeds in the `data/mapping/ subdirectory will use the marketing schema