As much as I do like Dune, I think in general, David Lynch films ought to have a disclaimer at the front of them; "Warning: The director of this film has a thing for bodily fluids, remain calm!"
But to answer your question, yes, the Harkonnen in the movie are much more...squishy than they are in the book and not nearly as sneaky. Rabban is actually about right (a mindless, sadistic brute who actually thinks he's the heir apparent) though Feyd-Rautha is supposed to be more of a dark, vain and spoilt reflection of Paul.
Having said all that though, while the "movie Baron" is of course much more extreme and psychotic, I think the original book version is actually allot more perverse, though you only get a little hint at the extent of his "tastes."
As for the cat...best not to ask. In the book they did impregnate Thufir with a poisen, but cat milking was defiantly not involved. Actually, if I remember it right, it was actually a precaution against his betrayal or escape and moreover he didn't know he'd been addicted as the Harkonnen were secretly feeding him the antidote. The idea being that to kill him, all they need to is withhold it.