The answer, thankfully, is yes. Because CivicSpace is, essentially, Drupal with several modules added on, and configured together (in the case of CiviCRM, this pre-configuration can save you some incredibly painful configuration / installation issues), all Drupal themes should work perfectly with CivicSpace without the need for any customized tweaking.
The system is the same, since CivicSpace uses Drupal's theming system. You can install any theme or themes that suit your aesthetic preferences, or roll your own, as long as you have the corresponding theme engine installed. I greatly prefer the PHPTemplate Engine so far for customizing drupal layouts.
Uploading and installing a theme is as simple as in a regular Drupal install, which I've already covered in my other tutorials. The process is identical.
