Can any HTML Editor be used with DDW?

It depends on what you mean.

Technically, ANY html editor can be used with DD for Web.

Now, in the
current version (DDW 1.10), there's not a direct connection feature (OCX, or whatever)
that will pump pages from the database into ANY editor (other than ours)
So, there is some piddling around that needs to be done to get it into the database
(either drag-n-drop to site manager, or read from file/save to db in DD-editor)

To make matters more complicated, when someone asks that question, it really
translates to:
Will my nice WYSIWYG editor understand and display the appscript appropriately.

the answer to this is basically "No." I've used MS FrontPage and Symantec VisualPage
and when you start putting in the appscript, the WYSIWYG features are pretty useless.
If you think about it, that's not so absurd. There is really no way that a WSYIWYG editor
(even if we wrote it) could display appscript appropriately, since it would have to actually
execute the pages to get their appearance, and then translate the HTML back to appscript.
Its the same functionality of a source-code debugger.

I'm also pretty certain that if you have any web developer that is the least bit sophisticated,
they are very seldom working in the WYSIWYG world. They are writing some kind of
dynamic content that won't display in the editor, either. (javascript, applets, asp, etc.)

The only unknown here is, of course, Microsoft. I don't know how robust and/or
integrated the Visual InterDev product suite is with respect to dynamic content
using ASP and VBScript .

My stock answer to this question is that, for my pages, I use VisualPage at the beginning
to get my layout right (frame layout, table creation, etc),
then switch to the DDW editor to do the scripting work.