SMTP Error: Could not connect to SMTP host
Doh! It turns out this was not a Drupal issue, but a Centos issue with SELinux. I was able to check SELinx settings by running the following commands

getsebool httpd_can_sendmail

which returned

httpd_can_sendmail --&gt; off

and

getsebool httpd_can_network_connect

returned

httpd_can_network_connect --&gt; off

I enabled them by running this

setsebool -P httpd_can_sendmail 1
setsebool -P httpd_can_network_connect 1

And the Drupal SMTP module worked beautifully after that. Hopefully this helps someone else as well.