I would say that yes if they can connect to the internet they would be useful. I personally have had both google home and echo devices. The echo device can be controlled from anywhere. I can be at work 60 miles from home and connect to my echo at home and play music from it because it does not rely on L2 connectivity.
On our campus we only allow airgroup for Apple TV and personal assistants, and other IoT devices, work without issue. Casting directly from one device to another doesn't work* without L2 capability as it is pulling from one device to another but if it can pull the content from the internet it can work and the users phone, tablet, or laptop can control the device.
Thanks for the reply. We also use a separate SSID for IoT devices. Are there already device signatures for Echo and Google Home in Clearpass or did you have to write them?
There are already signatures built into clearpass for both the google home and for the amazon echo. The google home will come in as a chromecast. The Echo on the other hand requires a bit more tuning after registered. I have found that all Amazon devices come in as an amazon tablet. It is fairly easy to change and I have trained our Help Desk to edit the device to an Echo and then it works without issue.
*The casting feature does work with the chromecast if you setup guest mode which enables casting while not on the same network. In that case they could be on their cell network and cast to a chromecast connected to the wifi which again is an L3 not and L2 connection.