According to their FAQ's:
Are my transactions secure when going through ebates.com?
Yes, our connection is in fact a secure SSL connection when you go to the checkout pages of any of our merchants. However, due to the fact that the merchant pages appear in a frame, the "padlock" icon may not appear at the bottom of your browser. Our engineers are aware of this and are working to fix this so as not to confuse our members. As mentioned above, we fully guarantee the use of your credit cards when shopping through ebates.com.