After a little experimenting I believe that what you're seeing are tracking attempts from websites using the in-app browser.
I didn't see a single tracking attempt when using Boost except when using the in-app browser.
If you click a link to http://amazon.com/ and it loads inside Boost then DuckDuckGo records the trackers that the Web page loads as coming from Boost.
I recommend instead using an external browser:
Settings > General > Default Browser > select "Open Externally"
A screenshot of the app was what I meant. But after posting that I tried it out myself (see my other reply).
I was kinda disappointed DuckDuckGo didn't give any meaningful insight. It looks like it's basically just guessing what the trackers may be collecting based on domains connected to.
As mentioned in my other reply I'm certain the trackers recorded are actually from opening websites using the in-app browser, not from Boost itself.