As far as I am aware, no one debates the fact that Russians have been fighting in Ukraine, what is debateable is if the Russian army has been fighting in Ukraine (whilst on duty, thus paid to do so by Russia)
It's not quite as easy to define as you would think!
That may be true but heavy equipment that is being used by the separatists is Russian. Also Putin in a interview for the Russian tv admitted that Russian army was involved in taking over the Crimea