The iptables man page says:
Using icmp-admin-prohibited with kernels that do not support it will result in a plain DROP instead of REJECT
I have been unsuccessful at finding out at which kernel version this became supported. Does anyone know?
FWIW, the server I am interested in is running:
2.6.18-409.el5 #1 SMP Fri Feb 12 06:37:28 EST 2016 x86_64 x86_64 x86_64 GNU/Linux