Kiddushin 15 - Hebew Servant Can Marry a Non-Jewish Slave-Woman
There are four categories of Hebrew servants discussed in the Torah:
1. A man who steals and can not repay, who is sold by the courts in order to pay the one he robbed;
2. A girl under the age of twelve who is sold by her father;
3. A man who sells himself because of his poverty;
4. A Jew who sells himself to a gentile.
A servant sold by the court can be given a Canaanite slave-woman in order to have children.
Even today there is a way for a mamzer (illegitimate) to have kosher children from a Canaantie slave-woman.