The short answer is no.
Once you activate Autoptimize’s Image Optimization, you’ll receive 500 free credits and you won’t need to create any account with ShortPixel. Once these 500 credits are used, a message should appear letting you know that you can receive another 1,000 free one-time credits (and 150 free monthly credits) if you create an account with ShortPixel.
Once those extra 1,000 credits are used, you can easily purchase more credits or keep using the 150 free monthly credits. You can find out more about our monthly and one-time plans here and here.