I do think that Daniel acted differently interviewing the vampires than he might with humans. Not that he's not fundamentally the same person no matter what, but rather that some of his abrasiveness and douchebag behavior isn't just because he's an old insensitive jerk, which he is, but because he is functionally being held captive by supernatural creatures who eat people and who have tried to kill him before.
"Save it for the rent boy." Daniel is not specifically trying to insult fake Rashid here. I mean he obviously does not care about hurting his feelings, but that's not the point of the line. He's telling Louis that he's not the stupid kid he used to be. He's saying look, I have immediately clocked that you're screwing the butler. Don't think you can trick me. I know what kind of rich person you are.
That line also hits worse because we know what Armand has been through but Daniel at that point does not. Daniel is also implied to have engaged in sex work as a young man so he's talking as someone who isn't there anymore, not someone who has never been there and never would be.
I know Daniel's a jerk and a hypocrite and that's what makes him fun but he's also the same guy who used to find people who fell through the cracks, who used to interview Kevin the disabled Vietnam vet who lives with his Vietnamese refugee boyfriend because those stories matter too.