>>96353092 (OP)
Depends entirely on the setting. In the earliest versions of what would become Judaism/Christianity, satans were just angels with a nasty job of being both tempters/judges, but God-sanctioned.
This is why in the Book of Job, which is the oldest book in the Bible, Big G and Satan interact in a way that's almost business-like or even casual rather than outright hostile.
Keep in mind that if going strictly by Christianity, all demons were once angels. Occult stuff like Ars Goetia has it that demons are still sorta metaphysically the same or almost the same as angels, just malevolent and depending upon the specific belief system with some debuffs/vulnerabilities forced on them by Big G.
In Nomine, THE tabletop RPG for playing Angels and Demons, in which one going against their nature (what incurs Discord depends upon the type of angel/demon) means spiritual integrity damage, actually has stuff for demons and angels allying.
Basically, it's like teaming up with people from the other side in a Cold War; usually more for mutual interest, convenience, or desperation. It's tense, either side is likely to betray the other, but genuine bonds can sorta form. But it's all hella risky and if your Superiors, either angel or demonic, find out you're all very much fucked.