Here's what I've found using WebDAV over an HTTPS connection within
Dreamweaver:

It does not work if you _only_ have an https connection to your server.
If you have both http and https, it will work, but some of the
information (specifically, the PROPFIND commands) go over the unsecure
http connection. I brought this to support Macromedia and I believe
they understand the problem and are looking to reproduce it. The
problem is whenever they've tested this in the past, they tested it
against a server with both http and https, and it works when set up that
way, so they think it's a config problem at the customer side.

FWIW, I am getting around this problem with a customized version of
"plink" that sets up a ssh tunnel through the internet that the WEBDAV
traffic passes through. DW thinks it's talking http and all is well.

John