That's pretty much it, woodpeckers drum to declare possesion of breeding territory in the same way a songbird uses its voice. They choose a dead branch or other surface for its acoustical properties. A dead branch that's still hard and solid makes the best drum, a telephone pole could fit that description.

When a woodpecker hammers into wood to find insects it's a less regular rythym. The bird is using it's beak more like a chisel than a drumstick and is often working on semi-rotted wood.