So the initial domains I was trying to work with were .ca domains. Remembering back to some issues I had with another provider, I tried a .net domain, and lo and behold, the WHOIS update worked. So it appears to be a bug/limitation with .ca domains, and perhaps others. At this other provider a year or two ago, they had to go in and make the WHOIS change, it wouldn't work from the control panel.
Lesson learned: .ca domains are hard (apparently).