Are you saying there would be a different domain for secure vs non-secure pages?
I guess the answer is I don't know as I'm not familiar with that kind of ssl arrangement. I would think being authenticated against secure.com is not the same as being authenticated against mydomain.com and would result in different cookies and I wouldn't think that would work but not for any reason specific to mojoPortal. If the whole site is at secure.com, then yes I think it should work.
If you try it let me know.