From the discussions with geist on IRC, it is more likely to be the other way around: Fuchsia may be borrowing some code from Haiku were applicable. At this point, it is a bit early for Fuchsia to provide us with drivers, they are just started on writing the kernel itself. I see only two drivers in Fuchsia at the moment:
https://fuchsia.googlesource.com/drivers/wifi/
https://fuchsia.googlesource.com/drivers/gpu/msd-intel-gen/
Both make heavy use of C++11, so adopting them in Haiku would exclude using them in the gcc2hybrid build. The driver API looks somewhat similar, which could simplify porting efforts. But, someone has to do the work, still.