Unfortunately, the answer is more a no than a yes.
NethServer “is” CentOS and it uses a version of dnsmasq that is built from CentOS.
RHEL/CentOS policy dictates that software version do not usually get updated, but the original software may be patched to support features from newer versions.
However, dnsmasq was updated to 2.76 in February 2017 by red hat.
So, it may get updated again in the future (I hope it does, I need a new feature, like you).
The usual route is to open an issue with red hat in their bugzilla or make your voice heard if the issue has been already opened.
I did a search (bugzilla.redhat.com) and I didn’t find anything about dhcp-relay.
You have a couple more options:
- find an updated package somewhere (there are famous repositories, use google)
- build the package yourself
In case 2, you can try to rebuild the package from Fedora, it usually works and it will adopted by CentOS in the future.
For 1, I couldn’t find a package, but you may have better luck with google.