GTK actually works smoothly on JLiMe (OpenEmbedded-based alternative GNU/Linux distribution) for the NanoNote, which has a slower processor than the Dingoo, and the Dingoo can be overclocked safely up to 430 MHz. Navigating the form without a keyboard could be hard, but then again, SiENcE's mouse emulation could help alleviate the problem.
The source code is probably open, have a look at the JLiMe website
, or ask a couple of questions in #jlime on FreeNode IRC, and I'm sure you'd get the source code for GTK.
I also heard some rumors about a possible JLiMe port to the Dingoo. You didn't hear it from me, but you could ask about that in #jlime aswell