There is and will never be an answer to your question. DotNetNuke is a "Content Management System" that manages the content and presentation that you provide.

Q) Is HTML ADA compliant? 
A) Not by default, but it CAN be.

For example, when you display an image on an HTML page it is *not* ADA compliant. If you use the alt tag with "Me and my dogs" it would be considered ADA compliant. If you do not use the alt tag or use less than meaningful descriptions like "image", the page is *not* ADA compliant. If you use a image that says "Click Here" without adding "Click here" in the alt tag the page is *not* comliant. Fancy mouseover swapping images or colours simply cannot be used by a blind individual.

If javascript menus hide actual functionality a simple workaround is to add the same links, usually to the left, right or bottom of the page to allow site navigation. A sitemap is also very useful for ADA compliance. Some sites may even provide a text only version but they are much more difficult to implement and maintain.

DotNetNuke provides various techniques to help your website be ADA compliant, but ultimately it is up to you to ensure the content meets ADA requirements.