Really? When did that change? It used to be that you could use it as a trigger for HomeKit routines, but not Alexa routines.
I know Amazon has been talking about opening up routines to button triggers, but I didn’t know it was active yet.
I just checked Amazon site and the Hue site and I don’t see any reference to Alexa routines for this device.
answering my own question, partially
woo hoo!
I went into routines in the Alexa app and, indeed, my hue hub-connected dimmer is available as a trigger! Not all options for all buttons, but still. Very very cool. Thanks for bringing this up, I had no idea. 
I don’t want to hijack this topic, so I’ve started a new thread on these new Alexa routine options:
Alexa adds more routine triggers, including buttons and lights