If it's a web page using HTML, the chumby does not display HTML.  Usually for chumby, one creates an HTTP service that supplies XML with the data one wants to display, then the Flash in the widget fetches that data, and does whatever it needs to display it.

As to tooling, it is indeed the case that it's now much more difficult to create Flash widgets, since Adobe has black-holed the entire development suite, and even if you had working licenses for older versions, their license server is also ignoring requests from those versions.

You may be able to find a working version of FlashDevelop out there, which would be enough to make widgets - indeed, the internal chumby developers, at least the ones that ran Windows, used that almost exclusively.

What I've done is maintain a bunch of old laptops, running old operating systems, running old versions of the Flash IDE.   It's a very clunky way to work - these machines are actually unable to do much of anything on the web since so much has changed, so I build the widgets on those machines, and then transfer them to and deploy them on contemporary machines.

Way back when, I compiled a whole bunch of Open Source Flash development tools for the chumby itself, so you could try to use that to create widgets.

A link to it is at http://wiki.chumby.com/index.php?title=Actionscript at the bottom of the page.