There is nothing inherently wrong with installing software that isn't
included in Trisquel. Trisquel doesn't include every single piece of free
software out there. For example tor is recommended that you install from
their PPA because it helps keep up with security updates.
You just have to be especially careful about installing non-free software
accidentally when it isn't from the repos.
I haven't checked out those drivers but source code availability does not
automatically mean it is free software. You also have to have the ability to
change and share it as well. You would have to check the license in that
case.
