I just wanted to pass this along to other DreamHost users.
Lately I have been getting periodic but regular "MySQL Error: Too many connections" and I noticed it seemed to be triggered by search bots.
After poking around for a solution to the problem, I learned that it is indeed caused by bots hitting the site too quickly and the solution was to add a crawl-delay to robots.txt.
I found the following to be most useful:
Hope this helps anyone else having the same problem.