Er, I’m sorry, but angels wouldn’t come to like any demon because of something like that!
Angels are just as selfish as demons, using humans to gain power. They don’t like humans, though they don’t really hate them either – they’re usually seen as inferior lifeforms to be exploited.
The only reason angels have a better reputation is thanks to previous mythology (false stories about how they’re gentle and loving), and the fact that their exploitation methods are generally not as brutal to humans as demon methods. Angels tend to try and sell themselves as benevolent creatures in order to gain more worship (how they gain power), which can lead to messy brainwashing and emotional/mental abuse… but that’s way less conspicuous than the demon who straight up rips people apart and eats their souls.
So angels aren’t morally superior, thus they wouldn’t care if Alcor homed dreams instead of nightmares. They’d probably react the same as other demons honestly – they’d think he’s weird and dangerous.
And let’s not forget that angels and demons are enemies! They fight over the same “food source” (humans), so they’re at odds with each other. The faith and positivity angels can instill in humans as a by-product of their worship mongering is toxic to demons; likewise, demons encourage and feed off of negative emotions that make things like faith/worship hard to do.
(Sorry, I don’t mean to shoot down your prompt, just wanted to clear up the misunderstanding!)