If I understand correctly: 1. if we don't use met5 in a macro (ie grep met5 in the DEF file doesn't appear on nets), we are OK for that macro. 2. if we use met5 in the macro for power routing, then we can also use met5 for normal routing. Short circuit will be detected in that case.

1. Correct. 2. Do you mean at a top-level or at the macro-level?

For 2, both: In some macros, I use met5 for power routing using the same width and pitch as the top-level.