Scaremongering aside, HarryT already made it clear that it is OK.
The tool is functionally similar to calibre's News Recipes feature.
Obviously you cannot redistribute them without violating e.g. CNN's copyright... but that has
nothing to do with the tool.
Now to actually answer your question
The only two EPUB --> MOBI/AZW3 converters are Amazon's kindlegen and the conversion code in calibre.
kindlegen is closed-source and Amazon doesn't offer ARM builds (how many people write and publish books
from their Kindle
).
calibre can be built under ARM but it has large dependencies.
I would say your best bet is to use calibre's source to write your own lightweight converter, possibly just regluing calibre's source code.
NiLuJe has published python builds for the Kindle (see the screensavers thread).