So Snape isn't an unskilled wizard, especially when it comes to defense as he was the Defense against the Dark Arts teacher. He very well could have dodged every attack Harry put to him simply because he was more skilled than Harry. But did the Felix Felicis at least help?
My immediate answer to this question when it came to my mind was no, because Felix Felicis only affects the user, but I don't think the evidence suggests this after all. For starters, the container of liquid luck that Harry gave to his friends was called a "small phial" and he had already used up one dose on himself prior to gifting it. There is no reference to the exact amount of liquid luck that Slughorn gave Harry, but I can't imagine based off of its description to be more than a few doses, so I'd assume there would be enough remaining for perhaps two or three people to take a mouthful at most. Despite this, Ginny says after the battle that no one died and remarks that this is due to the Felix Felicis. Certainly the two or three people who took the Felix Felicis in preparation for the battle would have had their lives spared as a result, but there were far more than two or three people battling for Hogwarts that day, including not only students but also teachers and members of the Order. This leads me to believe that the effects of Felix Felicis extend not only to the user, but any that is working in harmony with the user to accomplish their current goals. Unbeknownst to any battling at the time, Snape is included in this group of people that is working in harmony with Hogwarts, the Order, Harry and all those battling against the Death Eater intruders. With this being the case, it leads me to the question I am posing. Was Snape's impeccable ability to dodge the many attacks that Harry threw at him, some of which when his back was turned, simply due to his skill, or was the Felix Felicis working in his favor as well as he was an ally of those who took the potion?