A loan servicer is not considered a debt collector under most legal definitions. Debt collectors only come into play when you are sufficiently past due on a debt, whereas a servicer manages the loan while you are still paying it (although it can start the foreclosure process if you default on a mortgage).
This is an important distinction, as consumers have rights under the Fair Debt Collection Practices Act (FDCPA), which defines how debt collectors can act when trying to collect a debt from you.