Is it bad practice to use a built-in function name as an attribute or method identifier?

It won't confuse the interpreter but it may confuse people reading your code. Unnecessary use of builtin names for attributes and methods should be avoided.

Another ill-effect is that shadowing builtins confuses syntax highlighters in most python-aware editors (vi, emacs, pydev, idle, etc.) Also, some of the lint tools will warn about this practice.

Yes it's bad practice. It might not immediately break anything for you, but it still hurts readability of the code.

To selectively quote from PEP20:

Beautiful is better than ugly.
Simple is better than complex.
Readability counts.
If the implementation is hard to explain, it's a bad idea.

Seeing a call to myobject.dict() it would be natural to assume that it's going to return myobject.__dict__, or that myobject.id() returns the same thing as id(myobject)

It's possible for them to find out that they're wrong; but that will take time and effort and probably lead to some mistakes while they figure it out. Calling your attribute myobject.object_id_number is much longer, but makes it clearer that it's different to id(myobject)

No, that's fine. Since an object reference is required there is no way to have them shadow the built-in.