Yes provided your previous work and mentor formed part of your PER. That is if your work was suppervised by that mentor and you are using that work as part of your PER he/she can sign off your PER.
Yes you can if he/she supervised you and the work meets the criteria for being recognized as PER. Also make sure that your work mentor is eligible to be recognized as a suitable mentor by looking at the criteria that the workplace mentor must meet at the ACCA website.
Good Luck.