Is there a study to shows male dogs really enjoy breeding human females? > No.
But the answer to that is absolutely self evident and applicable to male dogs humping male humans and also silicone toys. > Yes they absolutely enjoy that.
Pretty much all mammals have very similar genital anatomy. Some animals for example dolphins even have a more evolved clitoris than a human. This means that sex is pleasurable for animals. If you have ever jerked off a dog that was horny and wanted to be jerked off it is very easy to tell that is was fun and pleasure for him. Because he will even come back for more.
These are basic feelings that ensure that animals want to mate and that the experience is encouraging the behavior.
Animals are not single board computers that blindly execute a behavioral pattern. This point of view is antiquated and has been demolished by science. Experiments and measurements show that dogs have the capacity to love us and that their intelligence it way above where people would like them to be.
In my experience my dog behaves drastically different around me and around female dogs. He asks me for sex in very different ways than a female dog and the whole act works differently with me than a female dog. This leads me to think that he does it for fun and knows it is for fun. This is also supported by the fact that a human female or a male or a silicone toy does not smell like a female dog in heat, yet a male dog is more than happy to hump it.
Some evidence shows that female bears mate with most males in the region to confuse the males into not knowing whether the cubs are theirs and therefore lower the risk of the cubs being killed by them.
But the realization of sex -> half a year of nothing -> cubs must be a learned behavior as animals do not have the means of explaining that so unless a male has the time to observe the consequences of sex and put it together, he will likely not know that sex is for the purpose of making puppies. In a lot of cases a male will have sex and move away potentially never meeting his puppies. So I do not think your dog thinks that he is putting puppies into you.