My housemate brought home a Hue Lux starter kit and a Wemo switch today, so I can answer my own question:
Yes, it works! The actual bulb (in this case, a $15 GE Link which is controlled by the Hue bridge) will act as a “man in the middle” between Echo and SmartThings, using the Big Switch smartapp.
The only problem is the delay. At my house, the time between giving a voice command to Alexa to turn off the Big Switch bulb and the time when SmartThings fires the Big Switch app and does whatever else I have associated with it is running about 4 minutes.
That’s fine for a lot of things for me, like turning stuff off at night, or when I leave the house, or some other use cases where a 5 minute lag between request and action is acceptable.
Obviously not great for use cases where you’re standing there waiting for something to happen. But for anything where the lag is acceptable, I now have Alexa voice control over anything I can run off a switch event. Which is actually pretty awesome. 
@Tyler this doesn’t get you guys off the hook for coming up with eventual official Echo integration, of course, but it does mean that right now SmartThings is a value add to Echo, not just the other way around.
p.s. I did run into one weird ST error…if I added the Hue Bridge to Echo before I added it to ST, ST wouldn’t save the bridge details in the device list. If I added it the other way around, no problem, both Echo and ST can control the bulbs. I reported that to support.