Community ads are an extension of the site. They are probably the most colorful and visible component on a site's home page (if/when you see them).
Community ads were created to allow "people" to advertise on Stack Exchange without paying money to do so, on the condition that the ads and their backing information are things the community would "want". On Stack Overflow the ads are restricted to open source projects, and have other restrictions too. On other sites the threshold is more relaxed. The underlying premise still stands, though:
The goal is to help visitors find out about the cool stuff your community is doing and help promote activities they find important. And it's all visible right there on the sidebar next to every question, and the homepage.
Community ads are there because they are what the community "endorses". It says: "We are Code Review, and we think this is good: LinkToABC" It should be drawing visibility to things the "Community" is doing, not isolated individuals. It should be promoting activities that would be important to the general community.
So, there is nothing inherently wrong with any ad posted to the ad-vetting post: Community Promotion Ads - 2015 (as long as it is not rude, offensive, etc.)
Remember, if an ad is not conformant with the goals of the Community Ads, then vote it down. If it is conformant, and it also is something you want the site to promote, then vote it up. If you are uncertain, or ambivalent, then leave it alone.
(Reminder: Community ads should .... help visitors find out about the cool stuff your community is doing and help promote activities they find important )
"Community Ads" means "advertising the community", not "things to advertise on the site".