In a recent interview between a reporter from the BBC and Murat Karayilan, the current de facto leader of the PKK, the issue of support for the PKK from Syria was raised. Karayilan denied that the PKK was receiving any assistance from outside forces, including Syria, and stated that the story was "baseless" and "coming from outside, from the Turkish government" (BBC). Huseyin Celik, deputy chairman of Prime Minister Erdogan's AK party in Turkey, however, recently made a claim to the contrary: "It's known that the PKK works arm in arm with Syria's intelligence organisation" (Telegraph).
As is generally the case in situations like this, the reality is clear. Certainly one side is making a factual error, but it's not clear which one. It's even less evident if such an error is the result of bad information or an overt act of deception. There are more than a few reasons why both the PKK and the Turkish government might make manipulative statements on this issue, with the PKK benefiting from the impression that they represent a widely popular movement among Kurds in Turkey and the government able to discredit them by claiming foreign control. Without any real proof offered by either side, however, it's nearly impossible to be persuaded by either claim.
Since the Kurdish population in the region spans Turkey, Syria, Iraq, and Iran (among others), I would be surprised if they weren't receiving some level of aid from outside of Turkey, but it seems unlikely that Turkey's claims of direct support from the Syrian government, embroiled in their own internal conflict, reflect a substantial truth. At the same time, though one has to wonder how an organization like the PKK could sustain itself in a military conflict spanning decades without some high-level access to outside forces. Perhaps some further digging might illuminate the reality underneath this all, but for the moment it all smacks of unsubstantiated propaganda to me.