One of the core purposes of DTM, like other tag managers, is to manage marketing pixels (often called marketing tags). Adding pixels via DTM would be the best practice.
In DTM, you'd make a page load rule that only fires on the specific pages you need. This page load rule would then insert the marketing pixel asynchronously.
Thanks Nikita. Yes, I agree adding the pixel via DTM, but in some case like LinkedIn pixels, its a best practice to add the code using the CMS tools and not through DTM.
So, I can either define the path on which I want to code to fire while creating the page load rule.