While driving, I may tell Google Search with my voice to "Text ". Google will ask me what the message is, and eventually after completing the required back-and-forth, my phone prompts me to select an SMS application for sending.
I'm presented with Messages (i.e. the default Android SMS app) and Google Voice, but Hangouts is not one of the options.
In other applications where I may "Share" something, Hangouts is an option there.
This is on a Motorola Droid Turbo with 4.4.4 Android. My old phone, a Galaxy S3, didn't have a problem using Hangouts, if I'm remembering correctly (I could be wrong though).
I should also note that in my System Settings, Hangouts is the "Default SMS Application".
Any ideas on how to get Google Search to use Hangouts?