Advil (ibuprofen) and Tamiflu (oseltamivir) are safe to take together. There is no listed interaction between the two drugs and there have been no reports of adverse effects when combining the two.
Tamiflu (oseltamivir) has very few reported drug interactions and is safe to use with most medications. One of the only listed drug interactions is with probenecid, an agent used for the treatment of gout.
As flu symptoms tend to involve fever and muscle aches, Advil (ibuprofen) is a good choice to use in conjunction with Tamiflu to appropriately manage symptoms while treating the infection. It is important to note that ibuprofen is also the active ingredient in Motrin. Motrin, like Advil, is safe to take with Tamiflu.
Lastly, Tamiflu is sometimes associated with causing nausea and GI upset. The same is true for ibuprofen. Taking both medications with food may improve tolerability.