Is there a way to block some IPs from visiting my site?
It is very easy to do via IP Deny Manager with CPanel on some other host providers, but dreamhost does not use CPanel.
Can it be done with Dreamhost?
Thank you in advance.
Yes, though you do it in the more traditional way by using an .htaccess file placed into the directory of your domain. This is the same thing that the cPanel routine does, it is just not “automated”.
You can see how this is done on DreamHost by looking at this DreamHost wiki article on .htaccess (allow certain IP addresses section).