they dont have a slayer but there are different types. the mystics, archers, rogues, arent too bad. macers are pretty hard. the one fencer almost impossible.
theres no slayer on any of them
its a really hard area. best to do with a group if you dont have advanced gear. i see mystics do ok with rising colossus, i use a bushido chiv dexter with healing and 75 percent life leech 100 percent mana leech on bladed staff. 170s stamina 20 swing speed on jewels 55 dci refined suit. its still very challenging.
I believe the Sampire captain is vulnerable to an Undead Slayer, but it's been a while since I was down there.
As far as the Captains, I've soloed a few myself. I've soloed (or attempted to) 4 in the past: Bard on my tamer, just ghealing my greater and occasionally casting on her. I also did a Fencer on my Mystic, summon a Rising, hide/occasionally cast directly, repeat. In Fel Blackthorn, I was fighting a Wizard on my Red and got her to half health (with ~74% SDI and Corpse Skin) before I needed to repair stuff. I attempted a Rogue on my Sampire, but I stopped hitting it & ended up dying.
For the other Melee class Captains (Macer, Archer, Swordsman, to name a few), I don't dare attempt them alone. They beat the ever-loving crap out of me, but you only need 3 chars to make every single one go smoothly. Get a greater to tank, SW Myst Mage for secondary healing/damage, and a Sampire. Unsurprisingly, Sampires are EXTREMELY effective against Captains when they can just do damage and not have to worry about tanking.