You should only need sudo access for this if the bundle install fails on mysql2, to update apt-get and re-install libmysqlclient-dev if necessary. You should be able to handle those parts from the correct location with your "admin" user, then do whatever you need again from your regular user the site is hosted on.
This article will walk you through setting up RVM with a full Rails stack on a regular shell account. There is no need to even add an admin user to your VPS to perform this install, and you get to leave all of your services fully managed!!!
http://wiki.dreamhost.com/RVM#Do_Magic
If you have any other questions please do not hesitate to ask us, you can send our support team a ticket here https://panel.dreamhost.com/index.cgi?tree=support.msg& or you can even hit us up for support on Twitter @DreamHostCare
Thanks!
Matt C
DreamHost Staff