Pass a logo to image module
Update

If one needs to obtain "JUST" the filename for theme logo for the active theme for any given domain in a domain access environment (as the OP found he needed to do), then the following code provides the image file name for the theme logo as $img_file.

$global $base_url;
img_path = theme_get_setting('logo'); 
$str_to_remove = $base_url . '/sites/default/files/'; 
$img_file = str_replace($str_to_remove, '', $img_path);


Original

Pass "theme_get_setting('logo')" as the path for the first php script?

&lt;?php print theme('image_style', array('style_name' =&gt; 'thumbnail', 'path' =&gt; theme_get_setting('logo'))); ?&gt; 


or rather - an amalgamation of the two - 

if (theme_get_setting('toggle_logo')) {
print theme('image_style', array('style_name' =&gt; 'thumbnail', 'path' =&gt; theme_get_setting('logo')));
}