This is an enhancement requested at FOSDEM 2003. eCos should be able to run under Linux in the same way as RTLinux, or more interestingly, Adeos... see <http://www.nongnu.org/adeos/>. For that matter, presumably it would be possible to port eCos *to* the Adeos nanokernel allowing co-existence with Linux.
This bug has moved to http://bugs.ecos.sourceware.org/show_bug.cgi?id=86522