vipw doesn't check to see if you gave a valid path to a shell, or whether a shell exists. What it does do is lock the file that's being edited in an attempt to prevent corruption from happening if someone else tries to edit the file at the same time.
It's possible that tcsh isn't installed, or is in a different path than bash; /usr/local/bin for example. If the OP had /bin/bash as a shell and merely changed bash to tcsh, and there's no /bin/tcsh... On my Fedora 13 laptop, I don't have tcsh at all.
Also, SSH may or may not care about /etc/shells. Traditionally that file is checked by ftp, but not ssh. On my Fedora 13 box, if I remove /bin/bash from /etc/shells, I'm still able to ssh in.
The OP's best bet is to have someone with root privs on the remote box edit /etc/passwd.