Actually neither of the operators I dove with accepted credit cards either and the ATMs in Sabang were strongly biased towards VISA vs MasterCard. Those who accept credit cards may impose some pretty steep surcharges to cover their fees.
Yes this is true but I always carry them anyway as I travel alone and it is an insured backup fund should anything happen to my cash or credit cards. You can get them exchanged for Philippine pesos at most banks and only some currency exchanges. The banks will give you the best rate. I carefully plan my trip around when and where I can access banks. Some banks are open on Saturdays or Sundays but with limited services such as cashing travelers checks. They will also demand to see your receipt (which you are supposed to keep seperate from your checks) and want a copy of your passport. Banks may also limit you to cashing 200-300 US dollars worth per day.