yes,  I bought a router from them before and received the rebate check without any problem.
I think you have two options:
call the rebate center (find the number on the rebate form or the letter (post card) the send you), ask their fax number and send the UPC by fax (usually you can get your rebate validated faster this way)
Send a copy of the UPC with the post card then sent you and wait them to update the record for you.