I'm also using WP-LESS.
W3TC works just great for everything except minification. I get the following error *within* one of the resulting minified files (so note that the file is generated, but the contents are where the error lies):
Warning: Cannot modify header information - headers already sent by (output started at /public_html/example/content/plugins/w3tc-wp-loader.php:2) in /public_html/example/content/plugins/w3-total-cache/lib/Minify/Minify.php on line 325
325 is dealing with adding headers to the file My presumption is that his has to do with the directory structure. I don't think WP-LESS is a factor because these errors appear in both the CSS and JS minified files.