I tend to agree that it's okay/permissible. However, that doesn't necessarily mean you should do it. You'll have to weigh which you care about more: irritating some of the users who read your post (who feel like they're being constantly advertised to), or driving traffic to those sites/proposals. Keep in mind especially that since sites are pretty specialized, you may find yourself advertising to users who are unlikely to be interested; for example most physicists are not lawyers.
For what it's worth, I would find something like "Area 51 Law" a lot better than "Upvote Law Area 51 Proposal". Your current name is long, you're telling people what to do (instead of just letting them know it exists), and you can't even upvote proposals on Area 51.