At least one developer (cradek) is using [Redhat 9] with [RTLinux 3.2pre2].
Since Redhat 9 is based on a 2.4 kernel, it is a good choice for using or developing EMC1.
In order to install RTLinux you need to download [unmodified 2.4.20 kernel source] and apply RTLinux's kernel patch to that. Then build and install the kernel as usual, build and install RTLinux following its documentation, then build EMC according to the RtLinux build instructions.
For the EMC build, your nonrealtime PLAT will be linux_2_4_20 and your realtime PLAT will be rtlinux_3_2