This is a reasonable concern, but after having used Nim for a couple of years I have never run into this as an actual issue. The benefit of being able to keep your entire program in one casing style outweighs these concerns. For that is the purpose of this style insensitivity, to allow you to use a library using snake_case in a project using camelCase and the other way around. And after having used Python with mixed case libraries I must say it is a good solution.
Now back to your concern of identifiers being read in different ways meaning different things. Once you know that this will be an issue you tend to think about it when naming your variables, and so it tends to not really be an issue. The thing is that once you get used to it you know that `pidTarget` and `pIdTarget` is the same thing, so you either relax you expectations, or you don't construct your names with this ambiguity. And besides, a "pointer to a target id" and a "scalar process id" probably don't share the same type, so the compiler should be catching that anyways if you ever used it wrong.