Thanks to Florian Schmidt, we have anonymous editing available in the alpha mode of the mobile website.
He asked me to take a look at the data and it seems as expected usage is low (since not many people use the alpha) but it does give us an idea of the sort of edits we might expect on mobile web (although the very act of getting to the alpha is a bit of a challenge so should be taken lightly.
The current strategy is to review anonymous editing via the mobile app, although personally I think this is dangerous to use as the sole basis, as when downloading an app, I might assume that the app can somehow be associated with my phone and this might lead me to be on better behaviour :)
Anyway you can find anonymous mobile web edits here [1]. At time of writing this gives us a sample of 10 edits [2] including 3 edits to the same article. The user that did 3 edits did constructive edits. The other 7 consisted of 4 constructive (or seemingly good faith edits and 3 vandalisms.
[1] https://en.wikipedia.org/w/index.php?title=Special:RecentChanges&hideliu...
[2] https://en.wikipedia.org/w/index.php?title=Naqshbandi_Hussaini_Golden_Chain&... https://en.wikipedia.org/w/index.php?title=St._Joseph_High_School_(Connectic... https://en.wikipedia.org/w/index.php?title=Dirt&curid=24494046&diff=... https://en.wikipedia.org/w/index.php?title=Neath&curid=290509&diff=6... https://en.wikipedia.org/w/index.php?title=Straight_Line_Stitch&curid=31... https://en.wikipedia.org/w/index.php?title=List_of_WordGirl_episodes&cur... https://en.wikipedia.org/w/index.php?title=East_Point_Mall&curid=1805507... https://en.wikipedia.org/w/index.php?title=East_Point_Mall&curid=1805507... https://en.wikipedia.org/w/index.php?title=East_Point_Mall&curid=1805507... https://en.wikipedia.org/w/index.php?title=White_Fence&curid=31049320&am...