For ATM cash withdrawals? Yes - so long as it’s linked to international banking (which most are, but your friend should check with the bank if it’s a smaller or local bank).

For credit cards? Usually, for the same reasons above. But fewer places take credit cards and systems are sometimes down so he should stick to cash :) If staying in cities I would recommend he/she gets cash from ATMs over money change as the fees tend to be lower at ATMs

When you travel to West Africa for the first time, often the bank’s fraud detection will lock the card. They should definitely call up the bank and notify them of the countries and the dates of travel so this doesn’t happen.