Is it permissible for someone who has repented of lying on their CV to utilize the experience they gained during their previous employment, and is the salary from that work considered unlawful?

There is no harm in mentioning experience gained from previous jobs, so long as it is truthful, containing no lies or deception. It does not matter that the previous job was applied for with a false CV, but repentance is obligatory for that lie, due to the Almighty's saying: "And avoid the word of falsehood," and the Prophet's (peace and blessings be upon him) saying: "The one who pretends to have been given what he has not been given is like one who wears two garments of falsehood."