IMHO a script with a '#!/bin/sh' shebang should not use any bash-isms at all.
So, I'd suggest NOT to link /bin/sh to /bin/bash
BTW, the bash.tcz extension appears to be a bit "confused" about the proper location of the .bashrc (and maybe also the bashrc) file. When doing 'tce-load -wi bash' one gets:
cp: cannot stat '/usr/local/etc/.bashrc': No such file or directory
chown: /home/tc/.bashrc: No such file or directory
It might be that the '.../tce.installed/bash' script needs just a careful review.