Honestly, I don't quite understand what you are referencing. But yes of course, slaves are able to be Christians as the story of Onesimus in the letter of Philemon would indicate along with Galatians 3:28. Marriage is not necessary for salvation (and in fact in 1 Corinthians 7 Paul advocates to remain unmarried and celibate). Also, if someone is being abused against their will, that has nothing to do with sex outside of marriage but a sin being committed against them.