The firmware loaded on the Digispark complies with all licenses necessary to be sold pre-installed, and can therefore be resold, distributed, etc.
The libraries included in the software, such as the DigiKeyboard library are subject to the licenses and your interpretation of those licenses - Digistump provides the library as free open source libraries, we do not pay so that people can use them commercially or make any effort to ensure they can be used commercially - if anyone uses them commercially that is up to them to determine.
Things like Karma Controller, which has a firmware using DigiKeyboard, provides the firmware as free open source software which the user can install on the Digispark from a source or compiled version - it is my understanding that therefore honors the licenses - but I am not a lawyer nor responsible for the legality of any firmware other than what is installed on the Digispark when it ships.
I've tried to make that as not legal speak as I can - in summary my I'd recommend you either 1) distribute your firmware separately as FOSS and make a kit with the Digispark. We can help you make a one click installer for the end user to put firmware on the Digispark when they get it or 2) obtain any permissions or licenses you need to distribute it on the device
Anything Digistump has written is FOSS (commercial or not) unless restricted by a legacy license from the code base - such as the V-USB license.