That source comes straight from Kiev, so hardly impartial or reliable. Just look at the photos sent to US congress as evidence of a Russian invasion of Ukraine! Of course the issue of the far right is something that Putin can use as a thin veneer of credibility for what they are doing, in the same way the US uses the 'defence of freedom and democracy' to go to war whenever it wants.
However Crimea is not a lawless war zone where you're putting extreme people in a extreme situation, just because Putin is taking advantage of the far right issue does not mean it isn't happening. Look at the Odessa massacre and how things turn very ugly when these ultra nationalists bump into Ukrainians who don't like the new government in Kiev. The far right ideology in Ukraine hates Russians and Poles the most, but of course you can't be far right without a dash of anti Semitism.
Have you actually read that article?
"It is short-sighted and formalistic to conclude that the Ukrainian far right is insignificant based on the lack of electoral success"
Parties like svoborda don't worry about votes, they simply ejected various pro Russian parties out of the building
Look at men like Dmitry Yarosh, a key figure in the 2014 revolution. He is a straight up fascist who claims he commands up to 10,000 men and is actively fighting in the civil war. He also claims, despite the ceasefire, his men will continue fighting as Kiev does not control them.
He was voted into office last October. So whilst the amount of far right politicians may be small, they have a lot guns and a lot of nutters who support them. If the US want to arm Ukraine then the only people worth giving them to are the far right, as the regular Ukrainian army is useless.