There are many ways you could acquire vegetation data to feed BRAT. You could use USGS's GAP dataset or in some states they have higher resolution vegetation layers, or you could classify your own imagery at higher resolution. For BRAT, we primarily use LANDFIRE's vegetation layers as our intputs. These datasets were derived from LANDSAT 30 m resolution imagery and their 'EVT' - existing vegetation type - layer does a surprisingly good job of characterizing the availability of suitable dam building materials for beaver even in small streams.
The video below walks you through the download.