I didn’t test it but it should work. FreePBX supports configuring it. Nethserver derives from centos which was used as base for asterisk/freepbx distros (elastix, trixbox etc).
Sangoma cards are compatible with most official Linux distributions and kernels (i.e. CentOS, Debian, Ubuntu) 32 and 64bit.
Sangoma recommends the use of CentOS as our R&D and QA departments use this distribution on a frequent basis.
Which pci card do you have?