Can I use Adobe Muse to create articles?

You can use any tool (Muse, Dreamweaver, etc.) to create HTML files. Then you use the HTML Article Packager to create the article file that you can upload to the DPS 2015 Portal.

What about InDesign? Can you have responsive HTML from exporting an InDesign document as .HTML instead of .Article?

I would imagine so, but with so many ways to create HTML why use InDesign?

In the words of Leanord "Bones" Nemoy from Star Trek, "Damnit, Jim, I'm a designer not a coder!" Now if DPS used BASIC, I'm down for that, I could do that, but I doubt they do and my HTML is about as good as my Japanese. End of line.

You don’t need to know any HTML to use Muse.

To underscore Bob's last comment, Muse was designed with the InDesign user in mind, focussing on design tools rather than developer tools to create web sites.

Yes but today Muse does not handle correctly the horizontal scaling of a whole page (only some objects). So forget Muse if you want the HTML to fit landscape/portrait orientations like a "standard" HTML page. Fixed DIV is not really the best method for multiscreen design and production.