8b kusi & eved go to galus and get malkos...Ritva s.v. Amai Kari bei asks that eved and kusi are not oseh maasei amcha...and eved also, even though he is amcha in that he's chayav in mitzvos like a woman, he's not allowed to enter the kahal [marry a ksheira]. The Aruch Laner has some problems with this Ritva, namely, according to this logic you could curse a mamzer or ger mitzri within 3 generations, but such a thing is not permitted! (I have some problems with his answer.)
I think there is a simple explanation. There are two types of people who may not enter the kahal: people who have a psul, like a mamzer, and people, like eved, who lack complete kedushas yisrael. Rav Chaim Brisker in Issurei Biah 13:12 discusses that an eved after his first tvila has to do mitzvos like a woman, but he does not have complete kedushas yisrael until after the second tevila, which happens after he is freed.
The Ritva does not mean anyone who is asur lavo bekahal may be cursed. He means even though eved is achicha in certain mitzvos, because he can't enter the kahal we see he's not fully b'amcha. But a mamzer who has full kedushas yisrael is certainly amcha.