The point is not necessarily whether it's morally wrong to violate a contractual agreement when the other party is likely to do so.

It's that the interview process proposed by the G[...]P may force the candidate to do things that may be illegal to pass the interview. The candidate is of course responsible for their own choices, but the point is that as an interviewer, if you force your candidates to do this, you might short list those who have a tendency to violate contract terms.

This might work out for some, but I'd say it's a fair point to bring up.