No, you don't need a GBA or NDS emulator to play Armor Mayhem. The only requirement is a PC with a good CPU since it's CPU-intensive and Adobe Flash to be enabled. You can play it in a browser like Chrome, Firefox, and even Internet Explorer. All of these browsers are compatible. You'll need a mouse and a keyboard to be able to control the character and the different orientation modes.
You can find the game on its official website. If Adobe Flash isn't installed or inactive, you will be prompted to do so.