i have to say some of the analysis here seems a bit too focussed on Right Sector, scum that they are of course along with the far right political parties.
there is no doubt some people in ukraine support the far right/nationalist movements. you can see it from the elections.
so when you get a mass movement - and it is pretty mass in scale - of people attacking the established political class - all the sides in the ukraine are corrupt and crooks, yanukovich, timoshenko et al, you are bound to get involvement from these people. there is also a huge wedge of evidence of people not in the far right supporting this movement and being there right now, tweeting, medics etc.
if the same thing happened in the UK you might well find yourself filling bottles with petrol next to someone from the edl or ukip.
rather like the revolution in serbia that outsed milosevic (with less violence).