I know it's been a while since you posted, but I wanted to reply.

I haven't read the manga in a long time, but no I don't think the crazy kid who always smiled was one of the ten. I think he was just super sensei in love with the bad guy but I don't really remember. I do wish they had shown more of the Ten Swordsman, especially the blonde guy because I think he actually joins the good side after Kenshin beats the snot out of him. I also wish the movie had shown what happens to the smiling kid, because his fate was kind of left out there if he died on the ship or not. 

Maybe they'll do something about it in the final two movies in 2021?