Hi @Ivangayton - thank you for asking to confirm, it is good to be certain about these things!
I have confirmed with several colleagues today (thanks @langstonsmith) that yes, it is acceptable within Mapbox ToS to use the Mapbox SDK without a Mapbox token. The Mapbox SDK is open source, so if you develop with it in such a way that does not require a Mapbox token that is fine.
That approach does limit how much we can be involved and supportive (if the implementation starts to fork away from our SDK it is hard to guarantee what we can support). But we would not see that as a violation of our terms.
If the best situation for the ODK community is to use a version of the Mapbox SDK without a token, but in such a way that creates the option for people to more easily use Mapbox basemap tiles in cases where people want to, that's 
by us.
(Perhaps it would be a good idea to include info for developers that fork ODK that it contains a modified version of the Mapbox SDK - and that if developers want the full-featured, updated Mapbox SDK they should return to the source for that. I wouldn't want to see a developer thinking that they were using the full Mapbox SDK without realizing that it was a modified version.)