Yes, the Yellow-bellied Sapsucker is a real bird. And I had one on my suet feeder this weekend during the cold snap in New England.
It was the first time I had ever had a sapsucker on a feeder of mine in about 20 years of birdfeeding. Plenty of other woodpeckers, but never a sapsucker before. I have, however, seen plenty of them in the woods among my wanderings, but never on a feeder before. Here are a few more photos of my visitor, none of which are great, but all serviceable. Notice how the bird is more streaked than our common Downy Woodpecker and how much more it blends in with the tree.