From catchbot.com:

Will my servers or site be affected by CatchBot?

It is unlikely that your servers or site will be affected by CatchBot. As Catchbot typically only crawls a few pages of any website slowly, CatchBot has no material negative impact on the load on your servers or the availability of your website.

…and by slowly they mean only 2 requests per second, even if the target URL is a 404 every time.