It's not inherently bad for someone to merit announcement threads since you might legitimately view them as particularly interesting and noteworthy. But some of those do look like a conflict of interest...
I consider getting merits on my services threads a kind of thanks from the given and an assessment of the service for everyone who wants to try it. Perhaps the real question is whether the merit source can send merits to ANN threads? Which has been answered here ----> https://bitcointalk.org/index.php?topic=3443147.msg35889040#msg35889040