For the most part if a debt is not listed on the schedules then the debt is non-dischargeable.  However, if the creditor receives actual notice of the filing then the debt may still be dischargeable.  A Creditor has 90 days from the first meeting of creditors to object to the dischargeability of a debt, so essentially, as long as the creditor was given enough notice to file an objection then the debt can be dischargeable.  If a collection agency is listed on the forms they act as an agent for the original creditor.  This should be enough to show constructive notice but in any case it is always safest to send a certified letter to the actual creditor if one is left out of the bankruptcy filing.

I strongly urge you to contact an experienced bankruptcy attorney to help answer specific questions relating to bankruptcy.  If you are in the New York City area contact my office at 212-244-2882 for a free, no obligation consultation.