They faced this Problem in 2014 already and decided to make them a regular part of their armed forces.@German is correct. The Azov Battalion is far right, and a sizeable contingent within that are Nazis. They were incorporated into the armed forces through necessity to fight the Russians after 2014. Unfortunately this does feed into Putin's lie about Ukraine being a Nazi country.
Zelensky must be holding his nose very hard as he calls them heroes. The real problems for the Ukrainian leadership will start after the war when they have to find a way to deal with them now they are regarded as heroes by much of the country.
That alone should tell you something