For your Entries type, it is as you suggest equivalent to Maybe. For me, the choice would come down to how accurately the names Nothing and Just (along with the name of the value in question) represent the data I’m talking about.
I will add another thing to think about from your example, though, and that is the type alias Id = Int. For this, I would use a custom type type Id = Id Int. This is because the custom type will prevent you from getting different ID types mixed up (for example, if there were type OtherId = OtherId Int, then the compiler would prevent you from providing an Id as an OtherId or vice versa), whereas a type alias will not.