Possibly, but Syria will deny it, and short of invasion we can't prove it. We know Syria had WMDs of their own and we did nothing about it.
You're right, and short of some special forces operation to deal with it, which doesn't seem very feasible, the only thing I can think of is a direct warning to Syria of a massive response if Hezbollah suddenly has WMD capability.
Something is stopping Syria from helping Hezbollah during this conflict to any significant extent.
Here's another thought. Perhaps we've already recovered those WMDs, but with an agreement with the Russians not to disclose that fact. In exchange for not publicly revealing the extent of their cooperation with Iraq in producing and hiding them, we got the WMDs but promised to keep the whole thing secret.
That might explain why the administration is being so quiet about the discovery of the 500+ chemical weapons found in Iraq. They're deliberately downplaying the entire issue instead of using that as vindication of the Iraq war policy.
Far-fetched perhaps, but I'm still looking for a reason why Syria is remaining docile in the current conflict if it's sitting on a cache of WMD.