If you install multiple conflicting modules with the same names exported you will get an error.
I found multiple modules named 'Graph'.
Module 'Main' is trying to import it.
Modules with that name were found in the following locations:
package elm-community/graph
package iosphere/elm-network-graph
package drathier/elm-graph
It seems to me that this could be caught at the time when you run elm-package install, it should be able to check if the code is already exported in the existing modules and warn you at least there might be a conflict.
Also when you are publishing a module, it would even be better to know that another module already claimed that space. That could be done by maintaining a database of exported names for key modules and warning you if you clash with them.
In the end I really want to be able to say from this package import this name under this other alias.
and there is an issue on that here Allow disambiguation when two packages expose modules with the same name