You can use Capture CC mobile app to create a brush then bring it into Animate CC where you can use that as a Pattern brush. You can refer to Draw with vector and pattern brushes in your animations | Adobe Animate CC tutorials for end to end workflow.
I know adobe capture and I've used it. I draw a rope and captured with the app. But it's a "black and white" brush so the outline of my rope is black, but the "internal part "it's transparent (see picture). So my rope is right but transparent, there are workaround to solve that like duplicate the layer and place a standard line below with the colour, but is too long for a production.
So if we have pattern brush with 2 colours in animate (like the geometric one) why a user can't do that with my own brush?
I've try to open the svg of the geometric brush in the animate 2015.2 folder to edit, but the result is odd, it lost the colours....
Any suggestion, workaround, ?