I started doing UBRS once daily after I saw this post, using the CM port to UBRS and just running in.
/tar The on entrance
/tar The in first boss's room (pre-pull)
/tar The after killing first boss
Today, I got a hit after killing first boss, screenshot here
I killed him and he dropped the pet (personal loot), but I'm fairly certain that isn't guaranteed unless you have it set to Need/Greed.
So to answer your questions:
1) First boss must die before The Lanticore spawns.
2) The Lanticore spawns in normal Heroic (just by running in to the instance)