I flagged one of my questions https://stackoverflow.com/questions/6359102/overriding-views-view-fields-tpl-php to request that mods move it to http://drupal.stackexchange.com but I think my request was denied/ignored. I'm not too sure how to tell but it has yet to be moved. Would it be wrong for me to re-post the same question on http://drupal.stackexchange.com? What's the proper etiquette for handling this?
You shouldn't cross post.
What you've done is correct. The moderators will have seen the flag - it could be that the one who dealt with it didn't agree, but I would take a request from the poster as meaning I should migrate straight away.
Raising the issue on the site's meta is the next step - another mod should review the situation.
If you do cross post it means that when the question is eventually migrated it will have to be merged, which is more work for the moderators on both sites.
Cross-posting the same exact question is not what you should do. If you were asking the question on SE sites with different topics, then you should adapt the question to better suit the site where the question is being asked. In the case where the same question is on-topic in both the sites as it is, I would suggest to flag it for moving it to the other site; if the question is not being moved after X days, then I would suggest to post a question here, as you did.
Keep in mind that the general rules are Don't migrate crap. and Don't push away your audience. to which you need to add the fact that moderators cannot migrate too old questions. This means a migration is not done just for doing it; there must be a good reason for doing it.
The question could also not be migrated, if the moderator who handles the flag doesn't think the question would be a great question for the site you are asking to migrate it. I am not saying your question is not a great or a good question; I am just suggesting what the moderator who saw your flag could have thought.