A computer can record most traffic on it's local network. Heck, you don't need a root kit for that. There are programs you can buy that will do this.
So yes, if your computer is infected it is possible that your iPad's internet traffic is being recorded. Any information sent from or to your iPad could be intercepted. This is why it is important to make sure all sites that you use with confidential or financial data are secure sites; using the https prefix and having a certificate. While this data can still be intercepted, it will be encrypted, and nearly impossible to decrypt.
Data on the iPad itself is still secure. The other computer can only see what goes in or out.