Thanks guys. Both right.
The start failed, but it was because I had started the services tool from the command line, as user tc. Without having examined the source code, I suspect cpanel starts the services tool as root, so services doesn't have to worry about explicitly starting the daemons as root. When I started services as root, it worked a little better - but still no green light.
I did a quick compare of the openssh start/stop script, against the tftp start/stop script and found that the one for openssh lacks the "status" functionality (which simply reports the pid of the running daemon, if any).
After adding the status functionality to the openssh script and running services as root, it appears to do work as expected.