Several more things to add to my Valen report:
The healing orb in the Spellhold dungeon, right before you fight Bodhi and turn into the Slayer, apparently counts as a non-evil priest, and will start saying, "What? You support this fiend?" as long as Valen is in sight. If you move her away though, you can use it to heal party members as normal.
The drow guards in the temple of Lloth in Ust Natha react the same way non-evil clerics do when they see Valen, and will attack you if she's visible. It seems strange that they'd be considered non-evil clerics.
Not necessarily a bug, but an exploit. You can prevent the sun from blighting Valen by using a Protection from Undead scroll on HER. The reason this works is because the "Blighted" status is actually self-inflicted. This lets you use her in combat in broad daylight. However, it also prevents Valen from using any of her quick items or other abilities until the protection is dispelled, so you have to heal her by other means.
This isn't technically a bug either, as much as an advisory about the game engine. If Valen kills an enemy with a level-draining hit, the enemy will shatter into pieces as if you'd used petrification. (Any level-draining finishing blow will do this.) Important quest items will remain, but all other treasure is destroyed. If you want to loot your enemies, switch her away from her claws to deliver the finishing blow.