It’s not. If you mean an extension cord with built-in ground and surge protection, that is.

If your amp had a ground in its power plug, we wouldn’t be having this conversation. If there is a surge in the actual power to the outlet, the surge protector might catch it. But since this is about surges inside the device itself, it means you should no longer actually touch the amp because you might get a shock. You can imagine that the higher the amperage flowing through the amplifier, the more dangerous this is.