A 'Pig' per-se is a clean-out plug that's sized to fit a pipe of a particular size. It's either pulled through a pipe with a tow cable, or pushed through a pipe using pressure. They're used in a lot of industrial applications where buildup or scaling is a problem. I've never heard of one being used in a pool.
I assume that 'Poly-Pig' is a plug made of some 'poly' (urethane, ethylene, propylene, etc.) material that they hope to drag or push through your pool plumbing in order to clean out all the buildup in your wallet.
Also, since you have an above ground pool, you can just remove the plumbing and inspect it if you think it needs it (which it doesn't).