If you install a theme on the Bitnami Lifray instance, you will not be able to use it on your sites since theme resources are not served by Apache.
I have tried installing the Liferay themes from the market and from a downloaded archive package, but the result is the same.
The theme's webapp gets deployed into the tomcat/webapps folder and Tomcat loads them as web applications. However, when you assign the theme to a site in Liferay, the site will not display properly because the browser gets 404 responses from Apache for the JS and CSS and image files (static resources).
Sidenote: I also had to fix a JAI classnotfound error as well to make themes deploy, but that is a separate issue.