Is it possible to use a different theme for just a section on the page?
Thanks Clive and Cromian for your input. Guess its not possible to actually use 2 different themes on the same page.

The simplest solution I found is to use one theme, then add 2nd ones css using drupal_add_css function. Then hope 2 CSS don't interfere too much and it's good enough without HTML part of the theme.