Do you honestly think the choice of EU president will bother the Russians at all? I suspect they couldn't care less, and policy-wise it makes no difference for them at all (of course).
Do Putin cares about anyone else than himself? If yes, Tusk will be somehow coordinating the EU sanctions against Russia, so he will be relevant.
Like ingemann and ag said, being new the top EU posts are very open in what are the associated duties and tasks, so it depends a lot on the personality of the person in charge. No one can really expect Tusk to behave like Van Rompuy.
There is also this time a clear difference in personality between the President of the European Council (Tusk) and the President of the European Commission (Juncker). They are not the same type of person at all and they may durably shape the distribution of tasks in the EU (until know, the "who does what?" question has been a big issue).
Note that the mandate is only 2.5 years long. It leaves room for someone else (we all know who I mean) to take the job in 2017.