You can use any texture you want, however that is the normal "spark" texture.
Obviously, the height and width is changable, as is the blend mode if you'd like.
If you want to make the spark go across the health bar you'd use hp:CreateTexture instead of pp:CreateTexture, and if you wanted it to go across the entire unit frame you'd use self:CreateTexture.
The spark will sync with your energy tick timer the first time you get an energy tick. This shouldn't be a problem when you're first logging in or zoning, but if you Reload your UI it could be a little off at first.