There's the http://cs.elderscrolls.com/constwiki/index.php/IsYielding function that returns 1 if the actor is currently in the yielding process. But I don't know about checking for a successful yield.
I have another question:
At one point in the Dark Brotherhood storyline, you're given the chance to wipe out everyone in the Brotherhood Cheydinhal sanctuary as part of a quest. But in the CS, Vicente Valtieri is marked as Essential. Now, IIRC, when you kill him during the quest, he does indeed stay dead. So, apparently his essential flag was set to 0 at some point. But does anyone know when that is, or what triggers it? I checked his attached script for anything essential related and found nothing. It does set the DarkVamp quest to either stage 115 or 116 that reference his being killed. But at what point did he cease to be essential and become killable?
EDIT: NM I found it. It's a result script in the 10th stage of the Dark10Sanctuary quest. setessential VicenteValtieri 0 I should've looked a little harder I guess.
The way i play animations in BloodLust for feed on awake ppl is to duplicate the animatio entries i need so i can setup my own conditionals. The feeding animations are in the Sleeping and Sitting groups. Just go down that branch and find the one you are looking for, take note of the KF file name and path.
go up the tree and create a child of the idles node, making sure it stays at the top of the tree (since your anims will only play on very specific conditions, it wont likely overidde any default game idles, whereas if it's the bottom of the tree, so idle may return true first and override your own... also careful when putting your anim group at the top of the tree(child of the main group) as all the siblings below will get an asterisk, this can be cleared later in the mod data menu, jsut ignore those changes)
create your new entry inside your new uniquely named group (example: RSanimgroup -> RSfeedanim)
uncheck the return file box on the group , but keep it on the anim
you'll probably be callign the anim fro ma script, so create a variable like "playfeed", on the group put a conditional to check if that variable is set to 1, so whenever you want to play it set that in the script to 1, call pickidle and then reset playfeed to 0 afterwards.
the anim should have 2 conditionals like if pcvampire == 1 && if actorid == player
If you need more details just gimme a holler, my feed on awake ppl works real well, all i have to work still is the correct positioning between player and victim ^^