Documentation: https://developers.facebook.com/docs/achievements/
Each achievement must possess a unique URL with the appropriate Open Graph protocol
<meta>tags. We will scrape the achievement’s unique URL and use the information provided in the tags to generate the Ticker stories. The Ticker stories will redirect to the achievement’s unique URL.
So each achievement simply needs an HTML file that has nothing but meta tags in it? That seems weird to me so I just want to confirm. Since you still have to "create" the achievement via an API call (different than awarding it to a user), I don't understand why that doesn't suffice.
What's your question? If it's 'do i definitely need a page with the meta tags for Facebook's crawler?' the answer is 'Yes'
You can generate the tags programmatically via URL parameters, and can redirect any non-Facebook-crawler users that hit those URLs somewhere else if you want