Yup I tried a blood drinking weapon and it said can't use this in your formTried ninja tiger build at Hythloth event season time ago.
Damage output is low without hit area. With hit area all imps are aggroed and killing my images very fast. So now tiger ninja is for Blackthorn only.
Developers nerfed ninja forms too hard. Also looks like blood drinker is not working with tiger form bleeding. At least I didn't noticed any slight change in my HP regeneration.
Out of ninja form only 1 skil is usefull in PVM : focus attack.
Was fun to try it.