Yes you can do this - you can for example have multiple .dhall files with shared “src” folders to reuse models.
I don’t know if there is some direct example of this out there but if you look for projects with a separate “test” source-folder and test-project you will see how to setup this.
Basically you set up .dhall files that include a common one (the Dhall language allows for that) and then compile with spago -x target.dhall ./path-to/main.purs ...
EDIT: here is a small section in the spago-documentation that explains a bit more about this situation with an example of such a .dhall importing another one (for common dependencies) - technically you only need to include the source-files though.