When sending emails through gmails smtp (smtp.gmail.com) do I need to setup DomainKeys and any other kind of email config?
How/what are you trying to send through gmail? Are you configuring a standard email client to work with a gmail address? If so, you're correct -- you don't need any special configuration.
Basic instructions on client setup is available here: http://mail.google.com/support/bin/topic.py?topic=12769
AFAIK, DKIM isn't supported yet on google app domains either.