I don't think so. I am pretty sure that I read that the first argument to
tunnel must be an address on the host server. Not sure where I read that
though as I have been doing a lot of research in the last day or two. I
couldn't find it in the man page.
Two points here: 1) the example I gave is adapted from the actual
working configuration I use; 2) in the man page example address C is
not mentioned at all in the configuration of "Router A". How can
router A divine it, as it obviously needs to send the GRE packets to
the address C (remote-outer-ip).