I haven't looked recently, but a while ago there were modified build.prop (build properties) files you could download. The build properties identify your device and its general specifications, which some applications used to authorize usage. This was the popular method for gaining Netflix functionality on 'unsupported' devices.
I'm not sure if it still works for Hulu/Hulu Plus. I do know that you still won't be able to watch videos/movies that aren't available for "mobile streaming" if you're using the Hulu app (even if you make it work on an unsupported device). The streaming requests reveal that you're using the app, although modifying Flash as well as a browser's user agent may allow for Desktop-only videos in the browser.
Re: Is a Modded Hulu/Flash baked into any of the custom roms?
If any ROM developer admitted to this being within their ROM it would get pulled since it would be illegal to circulate the ROM knowingly. So I would suggest not asking for illegal stuff openly on the forum but if you MUST find out ask them in PMs.