I mean if you do go buying the list and assuming it's just a list not an actual newsletter - you'll definitely need to work a lot on that before merging with your own newsletter.
It'd basically be a warmer-than-completely-cold customer acquisition source, and you'd have to approach those people with an option to sign up to your newsletter, tell them why it's a good idea and see if you convert. I would 100% recommend against adding any cold email list into your newsletter mix, you'll kill your deliverability