Then I really can't imagine why the call to poll.css isn't appearing in your source code... it uses the top hook and there isn't much that could go wrong other than another mod poorly programmed (with an = sign instead of .=) that "hijacks" the hook and doesn't let anything else on it.
You could try adding this line to your headinclude template...
Code:
<link rel="stylesheet" type="text/css" href="clientscript/vbulletin_css/style00090l/poll.css" />
That should manually include the poll.css file on this style for your board.