Yes, but it doesn't say so on Zotacs site and it would be an easy mistake to make. Anyway, I wrote to Zotac and they replied that:
"...yes it will work 🙂 . There's not much difference performance wise but if you have it, why not use it!"
So, that tells me that it will work but that I still don't know whether it's worth it, if the performance difference is really pretty small. Also, two DIMMs will apparently consume more power than one, even if each module is half the size, so that's something to consider if you're looking to build a _very_ low power system. So I'm off to look for benchmarks...