What makes you believe that it's Putin that's playing for that side, and not the other way around?
One thing that I'm actually seriously afraid of is that Putin will use the separatists to stage a coup inside the country. Consider this: right now, it seems clear that without outside intervention, rebels are doomed - Ukrainian forces grind them down slowly but surely, even despite the heavy losses. They know it full well, and they have been demanding help from Russian government since the declaration of independence - and then complaining that what they get is still not enough (which is true). Some of the lower-level commanders and rank and file have already been calling Putin a traitor on record. But never the top brass, like Strelkov. In fact, Strelkov is pretty much always very deferential to Putin, and called him "supreme commander" on occasion.
Now, imagine what happens when the last stronghold is overrun. The remaining forces - doubtlessly, the most loyal and battle-hardened of Strelkov's troops - will try to retreat across the border into Russia. If, by some "miracle", they are allowed to pass safely through, what do we have? A charismatic leader, widely popular in Russia itself, with a clout of an almost-martyr for the cause that most people root for, valiantly and losing the battle only because of "traitors" - even if he's not pointing any fingers at them (just makes him that much more noble, hey!). And several thousand armed loyal troops at his command. Now, what if Putin declares that the only reason why he was not able to order a direct intervention and turn the tide is because of all the traitors in the government, and that he needs help purging them? Strelkov then turns the entire Dolchstosslegende around and says that, yes, the people who were complaining about treason were right all along, but Putin was not the traitor, the traitors were the one who bound him and prevented him from acting - and marches straight onto the Kremlin. No-one would stop him; heck, I know for sure that a lot of people would cheer, and most police and military units would just step aside if not join outright. Once he arrives, we have a bloody but brief purge, with some bodies displayed for the amusement of the crowd, and Putin is now officially a dictator for life, Defender of Holy Rus or whatever titles they decide to bestow on him, with his own personal loyal guard to protect him.