As far as I can think of, Orwell never comes out and says anything about this. However, if you look at his characters, more of the women are relatively human. In fact, we don't really see women who aren't "human" except for Winston's wife.
The woman we see most in the book is Julia. She has clearly retained much of her humanity. She wants to have fun and have a life. Another woman we see is the prole woman hanging up the laundry. She has also held on to enough humanity that she makes Winston think that the proles are the key to the future. Finally, we see women like Winston's mother and the mother in the lifeboat in the film. They are showing human emotion by protecting their children (or trying to).
So I do think Orwell is implying it's harder to dehumanize women. Possibly he thinks that women are more emotional and nuturing and therefore thinks they will retain more of an emotional life.
One other example to demonstrate that Orwell suggests that women are less susceptible to dehumanization is Winston's memories of his mother and sister. While his mother seems willing to sacrifice everything for her children, and while Winston's sister is the typical innocent child, Winston remembers himself as being selfish and petulant, almost absent of familial feeling, suggesting that he would develop into an adult who possessed very few human qualities.
What a great question.
If you take a look at what we know about general differences between women and men, Orwell might take the same notice that most of mankind does. Women are emotional, men are logical. In this regard, women could often be interpreted as experiencing more of humanity, but that doesn't necessarily make it true.
In 1984, I see Julia's emotion much more clearly than male emotion of any of the male characters. Julia has moments of a complete carefree spirit, rebellion, love, passion and fun. Winston struggles to have these but wants all of these. Thus, I do believe Orwell makes the suggestion whether intentional or not that women are less suceptible to dehumanization.
The consistent references to the woman outside who does her laundry and sings demonstrates less suceptibility to dehumanization as well. She maintains her regular duties and cares with fervor and pleasure. These are extremely human qualities that I don't think you see in animals, or as much in men. That's not to say men aren't capable of such, I just think you see it more in women.