Currently, if a Certify Code is added to a blog's <head>HTML via Settings > Website > Blog > Templates > Header HTML, it will not load on AMP pages because HubSpot blocks all <head> HTML and JavaScript files to maximize load speed.
At this time, Alexa AMP Certify JavaScript snippets cannot be implemented effectively on HubSpot blog CMS pages.
Currently, CMS AMP pages do not support <head> and <body customization or the amp-analytics element. (You can paste the codes in Settings > Website > Blog > Templates > Header HTML and Footer HTML, but the scripts won't be included in the AMP versions.)
I've passed your use case to the product team. While adding support for custom scripts on CMS AMP pages is in their backlog, "it's not something [they] expect to be able to address in the near term."
Currently, if a Certify Code is added to a blog's <head>HTML via Settings > Website > Blog > Templates > Header HTML, it will not load on AMP pages because HubSpot blocks all <head> HTML and JavaScript files to maximize load speed.