Yes you can use Auctiva and you do not need to worry about IP addresses or cookies. The only time you need to make sure things are different is when you are first setting up the Auctiva account with your Ebay account to get the Ebay token. If you are following the stealth guide and using seperate user accounts for each Ebay account then you should be fine and have nothing to worry about. Once the account is linked to your Ebay account you are good to go and don't need to worry about anything.