Slow blinking in cats is often thought of as an expression of affection by humans, but that is only half the truth. On its own, it is merely a signal communicating that the cat is not preparing for an attack.
Hissing typically communicates that the cat feels personally threatened, or perceives someone threatening her possessions. It is a clear sign to back away or face the consequences.
At face value, I would consider this as the cat communicating that it doesn't intend to start a fight, but at the same time warning the other party to mind their distance.
As for the dog's capacity to understand the message, I would assume that the general idea should get across clear enough.
While dogs and cats typically need some time to learn the finer points of the other species' body language, the signals here are somewhat similar in both species.
As far as I am aware, blinking and averting gaze for dogs signals they do not wish to interact.
As the hissing typically goes together with showing the teeth, the dog should clearly understand that the encounter is not friendly.
There will probably be details lost in translation, but the dog should at least understand that approaching the cat isn't what it wants.
