Support for Linux distributions other then Debian is available since 2011. FAI can install Linux distributions like Redhat, CentOS, Scientific Linux Cern, Fedora, openSUSE, SuSE, Ubuntu and of course Debian.
Read the announcement including a small HowTo.
Distribution specific stuff
Just get the basefile for Ubuntu from https://fai-project.org/download/basefiles/ and use the Ubuntu examples from /usr/share/doc/fai-doc/examples/simple.
FAI 4.0 includes examples for installing CentOS 5 and 6. Ready-made basefiles are available at https://fai-project.org/download/basefiles/. Sample log files for a CentOS 6 installation can be found here
Scientific Linux Cern
FAI 4.0 can also install SCL 5 and 6. Ready-made basefiles are available at https://fai-project.org/download/basefiles/.
RHEL5 and 6
Redhat Enterprise Linux 5 and 6
This should work in the same way as CentOS and SLC.
A more verbose description on how to do this with SLES9 is available here
Bootstrapping the base images for other distributions
Have a look at examples/simple/basefiles/mk-basefile. Works for Ubuntu, CentOS, SLC. For RPM based distributions it uses rinse, which also support some old versions of OpenSUSE.