I you have configured typography and colors for buttons in GP and add a GB button block you might be disappointed that you have to replicate everything again. If you even have custom CSS for the core button block, using the GB counterpart might even be more trouble than its worth.
Yes support this. The default should be that buttons inherit the theme button style, especially if using generatepress.
If you save your own templates locally, you can quickly retrieve various designs as well as buttons.