Hidden form elements are submitted with the form, so it won't have a value yet. That technique won't work.
Just add this to the top of your email body page:
global $connSiteDB, $WA_DFP_UploadStatus;
Then you can refer to the uploaded files in the email just like you do in the insert like:
<?php echo($WA_DFP_UploadStatus["WA_UploadResult1"]["WA_UploadResult1_1"]["serverFileName"]) ?>