loco, yes they are. You can create them in a decision before 1650 IIRC. To the OP, no I haven't played as them but I suggest trying them out, can't hurt.
Didn't we just have this thread yesterday, or the day before?
I played a game as Jerusalem in HttT once-- while I was considering switching my primary culture to al-Misr Arabic, I suddenly became leader of a PU with France and inherited the country shortly thereafter. I released most of the northern provinces as vassals and used it as a base to fund my enternal crusade against the heathens, and in recognition of the Lord's clear Francophilia I never switched cultures and instead began instituting settlement policies whenever I could.
KoJ can be pretty fun if you're lucky.