The link is to the blog submission form. I remember using that form when Google's blog search was new, to submit my blog.

I see that the page title is "Google Blog Search Ping Service", but don't see anything about an rss ping or an RPC ping url on the page.

I should've added the link to the API:
http://www.google.com/help/blogsearch/pinging_API.html

Ah, good. That is very useful.

So, to make a long API page short, the ping URL to add is

http://blogsearch.google.com/ping/RPC2 ?