Ol Scratch
Lieutenant Commander
Of course not, even with an inhibitor doodad, Artoo is sentient and a strong sense of what's right and wrong. When he was sold to Luke's uncle, one of the first things he did was trick Luke into take the inhibitor off so he could escape -- clearly being someone's possession isn't an option for him.Would R2 have served Vader in the absence of another owner?
He serves who he wants how he wants, just like any other free-willed individual. And just like any other free-willed individual, if you capture him and shackle him, he'll devote his resources to finding a way to escape that situation.
So, clearly, Artoo eventually discovers just how evil Vader/Anakin is and breaks off his relationship with him. No question about it.
As to why he didn't tell Luke or even Threepio? Probably similiar if not exactly the same reasons Ben and Yoda didn't volunteer the information.